The Disk Detective FAQ

We are proud to reveal today the answers to your Frequently Asked Questions (FAQ) about Disk Detective. Special thanks to Glenn, Katharina, Lily, Fer, Phillip, Maxim, Hugo, Doug, Michi, Ted and the rest of the advanced user group for helping put this together.

“The question is not if but how. The game’s afoot.”  –Sherlock Holmes

  1. How do you determine an object is a good candidate?

An object is a good candidate if it appears round in the DSS/Sloan and 2MASS images, shows no sign of multiple objects in the red circle, stays on the crosshairs, and is not extended beyond the circle in the WISE images. Of course you already knew that by reading the buttons—but here’s some more detail (below) about what those buttons mean.

  1. What is the “round” threshold?

A good candidate gives the impression of being round as you look through the flipbook, but the shape can look distorted in some of the frames. If it’s bright it might look “starlike”, surrounded by four spikes in the short wavelength images. Let’s look at a few examples.

Here’s an example of a good candidate where the shape looks distorted. The key is that the shape is distorted in different ways in different bands. Look at the DSS 2 image, for example. It’s distorted, even pixellated. But there are other stars in the field, and you can see that their images all look a bit distorted in the same way. That tells you there was a slight problem with the optics when this image was taken; it’s not that the object itself has a distorted shape.

Bright Star screenshot

This bright star is a good candidate, even though its DSS 2 Blue image (above) has four “diffraction spikes”.

Here’s a very bright star that’s a good candidate (show at right). Most of the objects you’ll see in Disk Detective are much fainter than this! At shorter wavelengths (DSS Blue, Red and IR), the star appears as a large disk with a cross of four spikes. Those spikes are starlight diffracted around the struts that hold the secondary mirror in place. They have nothing to do with what the star actually looks like.

Here’s another good candidate.  You’ll notice that the shape looks distorted in a few of the wavebands. For example, the DSS IR image looks a bit square—that’s what happens to those diffraction spikes for slightly fainter objects; they don’t appear as a cross, only as a distortion to the shape of the image. The 2MASS K image looks elongated. The WISE 1 image bulges to the lower left. But all of these distortions are different in different bands—so none of them count! You can only trust that you are observing a real astronomical phenomenon (as opposed to an issue with the telescope) if you see it in two bands.

For contrast, let’s look at this subject, which is NOT a good candidate. The shape is elongated, left to right, and though the shape changes a bit from band to band, you can see that it stays elongated in the same direction (except in a few bands).

  1. When do you say there are “multiple objects in the red circle”?

Let’s look at some examples. I count at least three background objects inside the red circle of this subject (besides the object in the center). These other objects could be contaminating the SED of the object we really care about, the one in the center of the circle.

This subject has an object sitting on the edge of the red circle, leaking light into the red circle. That counts! You’d have to click on “multiple objects in the red circle” for this one.

Just remember, a background object it only counts if you see it in two bands. Here’s an example. Clearly the DSS2 image of this subject shows some background objects inside the red circle. I see background objects at 1 o’clock, 4 o’clock, 7 o’clock and 10 o’clock (if the red circle were a clock face). Now, if you think any of these background objects appears in a second image, you would have to mark this as “multiple objects in red circle” not “none of the above/good candidate”. Indeed, if I turn my monitor all the way up, I can just barely still see the one at 7 o’clock in the DSS Red image as well, so I would mark this as “multiple objects in red circle”. (You might disagree.)

  1. How to know if an object is “extended beyond the circle”?

An object is extended beyond the red circle if it clearly has structure that extends beyond the red circle. A faint, smooth blue halo that extends beyond the red circle is OK. Let’s look at some examples.

This subject clearly has structure that extends beyond the red circle. It looks like it’s sitting in a cloud—and indeed it may well be sitting in a cloud of interstellar dust. Our Galaxy is full of interstellar dust that is not part of the dust disks we’re searching for. We often see objects on Disk Detective that consist of an otherwise dust-free star that just happens to be in front of (or behind) and unrelated blob of interstellar dust.

Extended_ScreenshotHere’s another one (shown to the right) that is extended beyond the red circle, a bit more subtly. Do you see the faint wisp of blue that connects the object in the red circle to the object in the lower left corner? That’s bad. It’s a sign that the SED is contaminated by light from that object in the lower left corner. Sometimes you have to squint and turn your monitor all the way up to see these.

  1. What do artifacts look like, and where can I find examples?

DSS images are from scanned photographic glass plates. Impurities such as dust or scratches can cause that some DSS images may contain strange objects. You can find examples of these artifacts here in this discussion.  In some images you’ll even see trails where an airplane flew overhead during the observation. Here are some examples of those.

  1. There is no “Redo” button. What happens if I have made a mistake?

It’s okay if you make a mistake now and then.  Each image will be looked at by several Disk Detectives before the final results are published. This process generally yields results that are remarkably free of errors and bias—much more so than when a single scientist looks at the data alone. So forge ahead and try again!

Here’s an interesting example of how a different Zooniverse project (Galaxy Zoo) used their classification data to calibrate and remove human biases that might otherwise have gone undetected.

  1. Where can I see examples of the most common SEDs?

Here is a blog post with examples of some of most common kinds of SEDs.

  1. Where can I find more information about the object I’m classifying apart from looking at the “Image”?

To find more information about the object you are looking at, look at the Talk page, where you’ll find the object’s Spectral Energy Distribution (SED) and a link to a page of information about the object in a database called “SIMBAD”. You can also try entering your favorite objects into the BANYAN II tool. Here is some more information about each of these resources.

I suggest starting by going to the object’s Talk page. To get to the Talk page for an object, click on the Talk icon:Talk_IconThere on the Talk page, you’ll find the object’s SED and a link to SIMBAD. The SED tells you where the energy is coming out as a function of wavelength; it’s an important tool for recognizing and classifying disks. Here’s a basic introduction to SEDs.  And here are some examples of common SEDs you’ll see on Disk Detective.

SIMBAD (Set of Identifications, Measurements, and Bibliography for Astronomical Data) is a big database of astronomical objects; you’ll find that about half of the objects on Disk Detective have entries in SIMBAD. Here’s more information about SIMBAD.

If you want to learn more about an object and it’s not in SIMBAD (SIMBAD give you a “No Astronomical Object Found” or “NoAO”), try another database, called “VizieR”.  Just type into VizieR the coordinates that pop up on the SIMBAD “No Astronomical Object Found” page and set the search radius to something like 2 arcseconds.

Note, however, that VizieR queries many different databases simultaneously and it may produce redundant or contradictory information!   When you see contradictory information on VizieR, check the dates of the references—it’s generally better to trust the most recent reference. Also, note that if there are multiple objects in the search radius (default 10 arcsec) they will all pop up in the query.  So you will have to take care that you are looking at the correct object.

VizieR contains lots of information we need to plan our follow up: the V magnitude, the J magnitude, the spectral type and the V band variability. So if you find a good candidate, it would be handy to grab this info from VizieR and mention it in a comment on Talk. Be sure to provide a reference and error bars, like a good scientist!

BANYAN II is another handy free online tool that’s not on the talk page. BANYAN II tells you if that star is likely to be part of any of several possible known groups of young stars.  That’s important because if it’s part of one of these groups that gives us a good estimate for the star’s age—and tells us that the star is pretty young (<100 million years old).  If the star is young that means the planets that orbit it are young–and hot–and easy to image!  So if BANYAN II tells you the star belongs to once of these groups, the star will probably be a good planet search target.

If the star is in SIMBAD, all you need to do it type the name of the star into BANYAN II. Press RESOLVE and the press SUBMIT and Banyan gives you an answer in the form of a list of percentages.

E.g. if I enter Bet Pic  (i.e. Beta Pictoris) I get something like this

PPV_TWA PPV_BPIC PPV_TUC PPV_COL
0.00 99.87 0.00 0.00
PPV_CAR PPV_ARG PPV_ABD PPV_FLD
0.00 0.00 0.00 0.13

In other words, the star Beta Pictoris is 99.87% likely to be a member of the Beta Pictoris moving group. Not a big surprise.

If I type in Gam Pic, however, I get this:

PPV_TWA PPV_BPIC PPV_TUC PPV_COL
0.00 0.00 0.00 0.00
PPV_CAR PPV_ARG PPV_ABD PPV_FLD
0.00 0.00 0.00 100.00

In other words, Gamma Pictoris is 100% likely to be a “field star”.  A field star is one that’s not associated with any group or cluster. Beta Pictoris, of course, has a well known directly imaged planet around it.  Gamma Pictoris does not.

If the star is not in SIMBAD, it takes a bit more work.  You have to type in the RA, Dec, proper motion, etc yourself.  You can get those data from VizieR.

If BANYAN indicates that a Disk Detective star is more than 80% likely to be a member of any of these groups (other than Field Star), we want to know. Make sure to comment about it on the Talk page!

  1. Why are there more object images than SED plot points?

The plot points in the SED show how bright the object is as a function of wave band—this kind of data is what’s called “photometry”. The photometry for most Disk Detective subjects in the near infrared and mid-infrared is quite reliable. This photometry comes from the 2MASS and WISE data; that’s what you see on the SED on the Talk page. The photometry at shorter (“optical”) wavelengths, however, is of mixed quality, so we left it off of the SEDs on the Disk Detective website for now.

However, we will need to incorporate optical photometry into the SEDs of the disks we discover to help us make better models of them. (This would be a good side project if anyone is interested!)

  1. How do I make a collection with my favorite objects?

Collect_buttonAfter you look through the flipbook on the main classification page, click on the “Talk” icon next to the “star” icon, it will take you to the talk page. On the upper left, you will see “collect”, click on it to add an object to a collection. You can then choose to add it to a collection called “Favorites” or you can click on “Start a New Collection”.

  1. Why can’t I see planets in the Disk Detective images?

Here’s a blog post with the explanation.

  1. Why are DSS images so pixelated? Why is there no DSS2 Image?PIxelatedDSS_Screenshot

Sometimes images from the Digitized Sky Survey (DSS) look pixelated like a cheap 1980s video game. Here’s an example (also shown to the right). That happens when there’s no bright object in the field, and all you see is the detector noise. That can happen when the object we’re looking at is either cool or behind a cloud of dust (e.g. when it’s in the plane of the Milky Way). It should still show up in the longer wavelength images, though. For more information about anomalies in the DSS, see this DSS website.

  1. How big are the images we see on Disk Detective?

In astronomy, the way we measure the size of objects on the sky is using arcseconds, and sometimes arcminutes. If you have 20/20 vision it means you can see letters that are 5 arcminutes tall, which corresponds to 300 arcseconds. Here’s a Wikipedia article with more information about these small units of angle.

The images in the Disk Detective flipbooks are 1 arcminute across (60 arcseconds). The red circle is 10.5 arcseconds, and the crosshairs are 2.1 arcseconds across. A super-human with good enough eyesight to make out an object the size of the red circle would have better than 20/1 vision.

  1. Why do most of the images seem to grow longer at larger wavelengths?

Here’s a blog post that answers this question.

  1. Some objects are noticeably bigger in the blue images than in the near IR. Does this indicate that they are more likely to be nebulae or galaxies than stars? How should we deal with them?

Some objects will look much bigger in the blue images because they are brighter at those wavelengths and they are saturating the detector (or photographic plate). When that happens, the central pixels in the image max out, and the object starts to appear much bigger than it would if the detector were behaving in a linear way. As we were saying in the answer to frequently asked question 2. (“What is the “round” threshold?”), these objects can also show diffraction spikes and other shape distortions.

All of this is OK and should not dissuade you from classifying something as a “good candidate”! Most objects that are saturated like this are stars, and they are sometimes the best objects for further follow up because they are bright.

  1. How do I join the Advanced User Group?

If you have done more than 300 classifications on Disk Detective and you’re eager to get more involved, send an email to diskdetectives@gmail.com and ask to join the advanced user group.  We’d love to have you!

Examples of SEDs

As we discussed in an early blog post, the SED (Spectral Energy Distribution) is a plot of how bright an object is are as a function of wavelength. You can find each object’s SED on its Talk page.

Tadeáš Černohous (TED91) put together a wonderful collection of some of the different kinds of SEDs that you’re likely to encounter on Disk Detective. Nice work, TED91!  Here it is for your delight. I added a few comments here and there.         –Marc

Early Type Stars (Debris Disks)

These stars are as hot as the Sun or even hotter, and generally have spectral types B, A, F or G. (Type O is even earlier than that, but these very massive stars are rare.) The SEDs for these stars are nearly straight, downward-sloping, lines because of the Rayleigh-Jeans law.  You’ll notice however that the very last point always falls slightly above the straight line; that’s because all the objects in Disk Detective were pre-selected for this property. This “infrared excess” is a sign that they might be surrounded by a disk, which glows only at these longer wavelengths.

enter image description here

AWI0006207, AWI00062ka, AWI00062aj, AWI0004y3p

More examples

Late Type Stars (Debris Disks)

These are stars of spectral type K or M, which are cooler and don’t emit as much at 1 micron as a the early type stars.  You’ll see that the first point of the SED is a bit lower for these objects. The physics of this phenomenon is the Wein Displacement law; the peak of the blackbody curve shifts to longer wavelenegths for cooler objects.

Another effect that can cause the first few points of the SED to drop is interstellar “extinction” or more specifically, interstellar “reddening”. That’s when interstellar dust between the star and the Earth absorbs some of the light at the short wavelength end of the SED.

enter image description here

AWI0005cm2, AWI0005mue, AWI0005m8k, AWI0005ag0

More examples
Young Stellar Objects (YSOs)

YSOs generally have more infrared excess than debris disks, and the excess kicks in at shorter wavelengths, even as short as K band. Many YSOs are also reddened by interstellar dust. The SED’s of these objects sometimes may look similar to those of Active Galactic Nuclei (AGN) and dusty red giant stars; it’s hard to distinguish among them. If you aren’t sure which one it is, try to find some information on SIMBAD or VizieR.

enter image description here

AWI0005wau, AWI0002ddn, AWI0002p0g, AWI0005wal

More examples

Saturated stars

See that point at 3 microns (fourth point from the left)? It’s “lower” than it should be. That sometimes happens when the light from a bright object “saturates” the detectors in the WISE 1 band. Most often, when you see this in the SED, you’ll also see that the WISE 1 image looks very misshapen or displaced from the crosshairs. These objects are NOT good candidates.

enter image description here

AWI0005ywh, AWI0005yuk, AWI0005x81, AWI0005zgc

Galaxies

The spectral distributions for galaxies can contain several components: stars of different types as well as dust at various temperatures.  Moreover, galaxies can be redshifted by the expansion of the universe, a process that shifts the SED to the right, sometimes even halfway across the plot. We aren’t interested in these objects in this phase 1 of Disk Detective, though we might be in the future.

enter image description here

AWI00009x3, AWI0000fsq, AWI00062j8, AWI0000an0

More examples

Quasars and Active Galactic Nuclei (QSO and AGN)

These objects may look like stars to you at first glance, because they often appear as a point sources of light. But these SEDs are clearly very different from those of stars. This is one of the ways SEDs can be useful! Quasars and AGN are also classes of objects we aim to discard in phase 1 of Disk Detective.

enter image description here

AWI00000t3, AWI00005z0, AWI00001hs, AWI00001m3

More examples

Planetary nebulae

Planetary nebulae have nothing to do with planets. They are clouds of gas and dust belched out by an old red giant star.  These objects are fascinating–but for the purposes of Disk Detective they are trash.

enter image description here

AWI0002dbc, AWI0005duo, AWI00006ju, AWI00059t3

Please note that all of these are just some common examples. The SEDs may be different from case to case, especially when those objects are somehow contaminated or blended.

Glosario en Español

Traducido por Hugo Durantini Luca, revisado por Fernanda Piñeiro. The English version is here.

ALADIN: Es una enciclopedia celestial interactiva que le permite a los usuarios visualizar imágenes astronómicas digitalizadas y superponer sobre ellas información de otros catálogos (obtenidos a través de SIMBAD o VIZIER). ALADIN puede ser utilizado desde su portal web o también desde una aplicación ejecutable java.

ALLWISE: El procesamiento de los datos de la misión WISE fue una tarea gigantesca y la información fue liberada al público en varias etapas. La publicación más reciente es la ALLWISE. Ésta es la fuente de las imágenes WISE que vemos en Disk Detective.

AGN (Active Galactic Nuclei / Núcleo Galáctico Activo): En el centro de cada galaxia se encuentra un agujero negro supermasivo. Cuando uno de estos monstruosos agujeros negros comienza a acumular mucho material, el proceso calienta el material alrededor del agujero negro, causando emisiones de luz dentro de un amplio espectro desde rayos X a Radio, este fenómeno recibe el nombre de AGN. Debido a que un AGN puede contener mucho polvo en ocasiones pueden imitar a las estrellas polvorientas que estamos buscando. Muchas veces somos capaces de descartar estos AGN usando catálogos como SIMBAD o espectroscopias de seguimiento.

Blend Object / Objeto Fundido: Esto se refiere a cualquier objeto observado en una imagen que en realidad está compuesto de dos o más objetos astronómicos distintos mezclados entre si. Esto puede ocurrir con imágenes con poca resolución espacial, o cuando nos encontramos con áreas donde se encuentra muchas estrellas y galaxias próximas entre sí. En Disk Detective intentamos descartar estos objetos.

Contamination/Contaminated object – Contaminación / Objeto Contaminado: Un “objeto contaminado” en Disk Detective es simplemente un objeto que presenta señales de varios objetos astronómicos. Ya que no tenemos forma de aislar lo que cada fuente está contribuyendo a un “objeto contaminado”, no consideramos este tipo de fuentes como objetos de interés.

Debris Disk / Disco de Escombros: Después de que una estrella termina de ingresar en la secuencia principal, un disco de rocas y polvo a veces puede permanecer orbitando la estrella durante cientos de millones de años. Este tipo de disco es llamado disco de escombros. Un ejemplo de estos discos es el cinturón de asteroides alrededor del Sol. La mayoría de los planetas extrasolares que han sido observado hasta la fecha orbitan dentro de discos de escombros.

Disk Detective Object of Interest (DDOI) / Objetos de Interés de Disk Detective: Cuando tú y otros usuarios clasifican un objeto como “ninguno de los anteriores/buen candidato”, el equipo científico lo revisa y si estamos de acuerdo en que está bien, es agregado a la lista de objetos de interés. Estos objetos entonces son clasificados y los más prometedores son enviados para observaciones de seguimiento.

IR Excess / Exceso IR: Una estrella rodeada por un disco circumestelar va a mostrar un brillo excesivo comparado con lo que sería una estrella desnuda, generado por la señal del polvo cálido emitiendo en el infrarrojo. Una forma común sistemas de disco en el cielo es buscando evidencia de este exceso infrarrojo. Todos los objetos que vemos en Disk Detective han sido preseleccionados por tener al menos un poco de exceso en el infrarrojo, específicamente en la banda WISE 4.

IR Source / Fuente IR: Una fuente IR es simplemente un objeto astronómico que presenta una señal detectable es la banda del infrarrojo. Cuando SIMBAD no puede reconocer un objeto como estrella, galaxia o algo familiar, a veces simplemente los llama fuente IR.

J-Magnitude / Magnitud J: Las magnitudes son una escala logarítmica que surgió cuando los astrónomos midieron el brillo de una estrella con sus propios ojos. La idea es que una estrella que se ve 100 veces más tenue que otra es considerada de una magnitud 5 veces más tenue. La “J” representa uno de los muchos filtros que los astrónomos utilizando para observar el universo en diferentes longitudes de onda. Particularmente el filtro J está especializado en la luz rojiza más allá de la capacidad de percepción del ojo humano, cuya sensibilidad alcanza su máximo alrededor de los 1.25 micrones (o 12500 Angstrom) de longitud de onda. La estrella Vega es comúnmente utilizada como punto de referencia, ya que por definición Vega tiene una magnitud de cero en la banda J, así que una estrella 5 magnitudes más tenue que Vega tendría una magnitud de J=5. Actualmente, todos los objetos en Disk Detective tienen una magnitud J <14.5. (Es decir que no son tenues que 1/631,000 respecto al brillo de Vega).

noAO: Esta abreviatura quiere decir “ningún objeto astronómico encontrado en SIMBAD”, simplemente significa que no hay ninguna fuente astronómica catalogada en la base de datos SIMBAD en ese conjunto específico de coordenadas. No quiere decir que no haya nada en esa posición; más bien es el resultado del hecho de que la base de datos SIMBAD solamente contiene catálogos estelares con estrellas hasta cierta brillantez dejando de lado fuentes muy débiles. Te darás cuenta de que alrededor de la mitad de los objetos de Disk Detective son noAO; ¡y en parte es por eso que estamos haciendo esta búsqueda! Pero cuando esto sucede en muchas ocasiones puedes encontrar más información sobre un noAO ingresando sus coordenadas en VizieR.

Parallax / Paralaje: Como la Tierra orbita alrededor del Sol, vemos a las estrellas desde diferentes puntos de vista en los distintos momentos del año. Ese aparente cambio en la posición de una estrella que podemos medir es llamado el paralaje de una estrella, un ángulo que generalmente varía entre 1 miliarcosegundo hasta 300 miliarcosegundos. Actualmente, el mejor y más grande catálogo de paralajes proviene de la misión Hipparcos de la ESA. De ahí es de donde provienen los paralajes citados en SIMBAD. Si uno divide 1000 por el paralaje (medido en miliarcosegundos) obtenemos la distancia hasta la estrella medida en parsecs. Simplemente recuerda que Hipparcos no trato de realizar mediciones más precisas que alrededor de 1 miliarcosegundo. Así que cuando el paralaje medido es menor a 1 miliarcosegundo, es mejor simplemente considerar que la distancia es > 1000 parsecs porque de lo contrario si hacemos la división obtenemos un sin sentido. La ESA lanzó una misión llamada GAIA para medir paralajes más precisos de una mayor muestra de estrellas.

Pre-main Sequence Star / Estrellas Presecuencia Principal: Una estrella presecuencia principal es un objeto que está en el proceso de convertirse en una estrella. Las estrellas nacen del colapso de una porción de una nube de gas molecular. Los objetos que están en este proceso de colapso se llaman estrellas presecuencia principal. Una vez que el colapso ha calentado la temperatura interna lo suficiente, la fusión de hidrógeno dará inicio en el núcleo, y en ese momento el objeto pasa a su fase de “secuencia principal”.

Proper Motion / Movimiento Propio: El movimiento propio es el movimiento aparente de una estrella en el cielo una vez que eliminamos los efectos de la rotación de la Tierra como así también los de la órbita de la Tierra alrededor del Sol (en realidad, la órbita alrededor del centro de masa del sistema solar, un punto que se encuentra dentro del Sol). El movimiento puede apreciarse debido a que el sol y otras estrellas poseen todas diferentes órbitas alrededor de la Galaxia. Por supuesto, cuando una estrella se encuentra muy lejos (digamos 1000 parsecs o más), resulta muy difícil apreciar el movimiento en lo absoluto. Por lo tanto, la amplitud del movimiento propio de una estrella dependerá de su distancia hasta la Tierra. En ocasiones utilizamos el movimiento propio como una especie de reemplazo para distancia; cuando una fuente posee un movimiento propio elevado, digamos > 30 miliarcosegundos por año, estimamos que se encuentra relativamente cerca del sol, aproximadamente dentro de los 300 parsecs. De todas formas es mejor cuando puede medirse el paralaje.

Quasi Stellar Object / Objeto Cuasi Estelar (QSO o Quásar): Este nombre se refiere a un objeto que reside fuera de la Vía Láctea pero aparece como un punto en casi todos los telescopios, al igual que una estrella. Usualmente se tratan de galaxias en donde el agujero negro supermasivo del centro está acumulando mucho gas y polvo, lo que hace que brille mucho más que la galaxia subyacente. Ver también AGN.

Saturated / Saturado: Al igual que las cámaras digitales y los iPhones en casa, las cámaras digitales astronómicas y detectores graban señales en una red de pixeles (cubos de recepción de luz). Si uno intenta tomar una fotografía de una fuente demasiado brillante, esos receptáculos se vuelcan y entonces nos referimos a ese pixel como saturado. Uno puede verlo estos todos los días cuando intentamos tomar una foto durante el día de algo cercano al sol (se producen rayas blancas verticales en la cámara digital). Las imágenes saturadas no son muy convenientes ya que nos impiden tomar mediciones exactas del brillo de una estrella. Esta estrella muy brillante (magnitud 6) está saturada en las imágenes DSS2 y también poco en la banda WISE 1.

Spectral Energy Distribution (SED) / Distribución Espectral de Energía:
Este término se refiere a la cantidad de energía que un objeto emite en función de la longitud de onda. Si medimos cuanta luz fue emitida desde un objeto a lo largo de todo el espectro, en un principio podríamos deducir los mecanismos físicos involucrados en cómo ese objeto brilla. Para las estrellas, la fusión nuclear en sus núcleos es emitida como radiación termal, la cual tiene una forma muy característica en los varios tipos de longitud de onda (también conocido como radiación de cuerpo negro). El polvo también emite térmicamente, usualmente al absorber una pequeña fracción de la luz proveniente de su estrella. Puedes ver un SED para cada tipo de objeto en Disk Detective en la página de Talk.

Shifting / Movimiento: Las imágenes de los objetos en Disk Detective a veces pueden aparentar estar moviéndose ligeramente de imagen a imagen. Esto puede ocurrir por ligeros errores en los registros entre imágenes o debido al hecho que algún objeto pueda tener una gran cantidad de movimiento anual a través del cielo (las imágenes DSS fueron tomadas entre las décadas de 1950 y 1980, 2MASS y SDSS fueron tomadas en la última parte de los 90 y principios de la siguiente y las imágenes de WISE fueron tomadas entre 2010 y 2011). En ocasiones puede ver un movimiento en un cambio en la luz en WISE 1 debido a saturación. Los movimientos más notorios son causados por contaminación- Ver también contaminación-

SIMBAD: Es una base de datos astronómica basada en la web que nos permite buscar estrellas por sus nombres o coordenadas, y acceder a gran cantidad de información como el brillo (magnitud) en varios filtros, coordenadas actualizadas, la velocidad a la que la estrella se está moviendo (el movimiento propio o velocidad radial), la distancia (paralaje), y publicaciones científicas que mencionan a esa estrella. SIMBAD significa Set of Measurements, Identifications and Bibliography for Astronomical Data / Compendio de Medidas, Identificaciones y Bibliografía para Datos Astronómicos.

V-magnitude / Magnitud V: La letra V representa a otro de los muchos filtros utilizados por los astrónomos para observar al universo en diferentes longitudes de onda. Particularmente, el filtro V se especializa en la luz cercana al límite del espectro de nuestro propio Sol, cerca de los 0.55 micrones (o 5500 Angstrom) de longitud de onda. Ver Magnitud J para nuestro intento de definir “magnitud” o también Wikipedia.

Variable Star / Estrella Variable: Una estrella es clasificada como estrella variable si su brillo en cualquier longitud de onda o filtro de paso de banda cambia con el paso del tiempo. Si pudiéramos medirlo con la precisión suficiente, veríamos que cada cualquier estrella es variable en algún nivel. ¿Qué podríamos esperar de una pelota de plasma experimentando fusión nuclear mientras rota? Pero realísticamente la mayoría de las mediciones no pueden detectar variaciones en el brillo si son muy pequeñas. Así que la mayoría del tiempo podríamos decir que una estrella variable es aquella cuyo brillo cambia más allá de un ligero porcentaje de una observación a la otra. A menudo mencionaremos la variabilidad en las magnitudes. Una variación de magnitud representa un cambio en un factor de aproximadamente 2.5, lo cual es bastante grande. Imagina que un día nuestro sol cambiara su brillo de tal forma. De todas formas este nivel de variabilidad y más es común entre estrellas jóvenes y entre estrellas gigantes, por ejemplo. Si el nombre de una estrella comienza con dos letras mayúsculas, como RR Tau, entonces se sabe que es una estrella variable (aunque existen muchas estrellas que escaparon a esta designación).

VIZIER: Es una base de datos astronómica basada en la web que nos permite consultar más de 13,000 catálogos astronómicos de literatura revisada utilizado su posición astronómica o nombre. El tipo de información que puede encontrarse en estos catálogos va desde el brillo del objeto a un amplio rango de longitudes de onda (desde rayos X al infrarrojo), entre otras propiedades.

WISE: El Explorador Infrarrojo de Campo Amplio de la NASA o WISE (Wide- field Infrared Survey Explorer), es una telescopio especial que fue lanzado en 2009 para realizar un registro de todo el cielo en cuatro pasos de banda en el infrarrojo: 3.4 micrones, 4.6 micrones, 12 micrones y 22 micrones. El proyecto de Disk Detective está minando el catálogo WISE para detectar nuevos discos de escombros y protoplanetarios. La misión WISE tiene su página en la NASA y otro en la universidad de Berkeley.

Young Stellar Object / Objeto Estelar Joven (YSO): Ésta es una abreviatura para cualquier estrella que aparente encontrarse en su fase de formación. Podemos pensar en estos como en estrellas bebé que por lo general no se encuentra muy lejos de una nube molecular, que es donde se forman las nuevas estrellas. Pueden tener chorros de material, grandes discos y una luminosidad variable a medida que expulsa gas y polvo de sus superficies. Los YSO pueden ser clasificados de acuerdo a su SED en objetos Clase 0, Clase 1, Clase II y Clase III. También se incluyen en este grupo los discos transicionales y “pre-transicionales” y otras rarezas interesantes. Ver también Estrellas Presecuencia Principal.

Disk Detective Glossary

Lily (voyager1682002) suggested that we put together a glossary of some of the jargon we use in Disk Detective.  Shigeru, TED91 and Pini2013 all contributed words and John Debes and John Wisniewski wrote up the definitions.  Nice work, everybody! If you think of any more words you want to see defined here, put them in the comments or send ’em in to diskdetectives@gmail.com

Marc Kuchner

ALADIN. ALADIN is an interactive sky atlas that allows users to visualize digitized astronomical images, and overlay data from astronomical catalogs (retrieved via SIMBAD or VIZIER).  ALADIN can be accessed both via a web-portal, as well as via a stand-alone java app.

ALLWISE. Processing the data from the WISE mission was a huge task, and the data was released to the public in several stages.  The most recent release is the ALLWISE data release. That’s the source of the WISE images you see here at Disk Detective.

Active Galactic Nuclei (AGN).  At the center of each galaxy is a supermassive black hole.  When one of these monster black holes starts accreting a lot of material, this process heats the material around the black hole, causing it to emit light across a broad range of wavelengths from the X-rays to radio, a phenomenon we call an AGN.  Because AGN can contain a lot of dust, they sometimes can mimic the dusty stars we’re searching for.  But we can often weed out these AGN using catalogs like SIMBAD or follow-up spectroscopy.

Blended object. This refers to any object observed in an image that is actually comprised of two or more distinct astronomical sources.  This can occur for images that have low spatial resolution, or in areas of the sky where many stars or galaxies reside together.  Here at Disk Detective we are trying to weed out blended objects.

Contamination/Contaminated object. A “contaminated object” in Disk Detective is simply an object that represents a mix of signals from more than one astrophysical source.  Since we do not have an easy way to isolate the contributions of each of the object contributing to a “contaminated object”, we do not consider such sources as viable candidate objects of interest.

Debris Disk.  After a star finishes collapsing onto the main sequence, a disk of rock and dust can sometimes linger around the star for hundreds of millions of years.  This kind of disk is called a debris disk.  One example of a debris disk is the asteroid belt around the Sun.  Most of the extrasolar planets that have been imaged to date orbit within debris disks. Disk Detective is primarily a search for Debris Disks and YSO disks.

Disk Detective Object of Interest (DDOI). When you and other users classify an object as none of the above/good candidate, the science team reviews it and if we agree that it’s OK, we add it to the list of Disk Detective Objects of Interest. These objects then get sorted and the most interesting ones get sent out for follow-up observing.

IR Excess. A star surrounded by a circumstellar disk will exhibit an excess of brightness in the infrared above that expected for a bare star, caused by the warm dust emitting thermal heat at these wavelengths.  A common way to identify disk systems in the sky is to search for evidence of this Infrared (IR) excess. Every object you see in Disk Detective has been preselected to have at least a small amount of infrared excess, specifically in the WISE 4 band.

IR Source.  An IR-source is simply an astrophysical object that exhibits a detectable signal at infrared wavelengths. When SIMBAD doesn’t reconize an object in as being a star or a galaxy or something else familiar, it sometimes calls it an IR-Source.

J-magnitude.  Magnitudes are a logarithmic scale that comes from when astronomers measured the brightness of a star with their own eyes.  The idea is that a star that looks 100 times fainter than another is considered to be 5 magnitudes fainter.  The “J” moniker refers to one of many different filters astronomers use to observe the Universe at different wavelengths.  In particular, the J-filter is centered on light redder than what the human eye can perceive, with a sensitivity that peaks roughly around 1.25 micron (or 12500 Angstrom) wavelengths of light.  The star Vega is commonly used as the reference point; by definition, Vega has a magnitude of zero in J band, so a star 5 magnitudes fainter than Vega would have a magnitude of J=5.  Currently, all the objects in Disk Detective have J magnitude < 14.5.  (I.e. they are no fainter than 1/631,000 as bright as Vega.)

noAO. This acronym stands for “no astronomical object found in SIMBAD”, and simply means that there is no cataloged astronomical source in the SIMBAD database at a specific set of coordinates.  This doesn’t mean that there is nothing at that position; rather, is a by-product of the fact that the SIMBAD database only catalogs stars down to a certain brightness and misses faint sources.  You’ll find that about half of the objects in Disk Detective are NoAOs.  That’s part of why we’re doing this search!  But when you come across an object that is a NoAO, you can often find more information about it by typing its coordinates into VizieR.

Parallax.  Since the Earth orbits around the Sun, we see nearby stars from a different point of view at different times of year.  The apparent shift in the star’s position that we measure is called the star’s parallax, an angle usually ranging from about 1 milliarcsecond to about 300 milliarcseconds.  Presently, the biggest and best catalogs of parallaxes come from from ESA’s Hipparcos mission. That’s where the parallaxes quoted in SIMBAD come from.  If you divide 1000 by the parallax (measured in milliarcseconds) you get the distance to the start measured in parsecs.  Just remember that Hipparcos was not about to make measurements more accurate than about 1 milliarcsecond,  So when the measured parallax is less than 1 milliarcsec, it’s better to simply consider the distance to be > 1000 parsecs because when you divide you’ll get nonsense.  ESA has launched a new mission called GAIA to measure more precise parallaxes for a larger sample of stars.

Pre-main sequence Star. A pre-main sequence star is an object which is in the process of becoming a star.  Stars are born from the collapse of a portion of a cold cloud of molecular gas.  Objects in the process of collapsing from a molecular cloud are called pre-main sequence stars.  Once the collapsing object has heated to a sufficient internal temperature, hydrogen fusion will begin in its core, and the object is thereafter formally classified as a “star” that resides on the “main sequence”.

Proper Motion. Proper motion is the apparent movement of a star on the sky once you have subtracted the effects of the Earth’s rotation and Earth’s orbit around the Sun (actually, orbit around the solar system’s center of mass, a point that is inside the Sun).  The motion arises because the sun and other stars all have different orbits around the Galaxy.  Of course, when a star is quite far away (say 1000 parsecs or more) it’s very hard to see the star move at all.  So the amount of proper motion a star has depends on how far away it is from Earth.  Sometimes we use proper motion as a kind of proxy for distance; when a source has high proper motion, say > 30 milliarcseconds per year, we expect it to be relatively close to the sun, roughly within 300 parsecs or so.  It’s better when you can measure the parallax, though.

Quasi Stellar Object (aka QSO or Quasar). This name refers to an object that resides external to the Milky Way but appears point-like in most telescopes, like a star.  These are usually galaxies where the central supermassive black hole is accreting a lot of gas and dust so it shines many times brighter than the underlying galaxy.  See also AGN.

Saturated. Just like your digital cameras and iPhones at home, astronomical digital cameras and detectors record signal across a grid of many pixels (light bucket receptacles).  If one tries to take a picture of too bright of a source, these receptacles will overflow and we refer to these pixels as being saturated.  One can see saturation in everyday life when you try to take a picture of an object in the day-time sky too close to the Sun (this will produce a vertical white stripe on your digital camera).  Saturated images are undesirable as one typically can not extract accurate measurements of a star’s brightness from a saturated image. This very bright (sixth magnitude) star is saturated in the DSS2 images and somewhat in the WISE 1 band as well.

Spectral Energy Distribution (SED).  This term refers to the amount of light an object emits as a function of frequency or wavelength.  If one were to measure how much light was emitted from an object across the full electromagnetic spectrum, on in principle could deduce the physical mechanisms involved in how that object shines.  For stars, the nuclear fusion in their cores is emitted as thermal radiation, which has a very characteristic shape across the various wavelengths of light (also known as black body radiation).  Dust also emits thermally, usually by absorbing a small fraction of light coming from the host star.  You can view an SED for each object in Disk Detective on its talk page.

Shifting. Images of objects in Disk Detective can sometimes appear to move around slightly from image to image.  This can occur from slight misregistrations between images or the fact that an object might have a large amount of yearly motion on the sky (DSS images were taken in the 1950s to the 1980s, 2MASS and SDSS images were taken in the late 90’s to early 2000’s, and WISE images were taken in 2010-2011).  Sometimes you’ll see a light shift at WISE 1 caused by saturation. Large shifts usually are caused by contamination. See Contamination.

SIMBAD. SIMBAD is a web-based astronomical database that enables one to search for stars by their names or coordinates, and retrieve a wealth of information such as the brightness (magnitude) in various filters, updated coordinates, the speed at which the star is moving (proper motion and radial velocity), the distance (parallax), and scientific papers that mention the star. SIMBAD stands for Set of Measurements, Identifications and Bibliography for Astronomical Data.

V-magnitude.  The letter V refers to one of many different filters astronomers use to observe the Universe at different wavelengths.  In particular, the V-filter is centered on light close to the peak of our own Sun’s spectrum near 0.55 micron (or 5500 Angstrom) wavelengths of light.  See J-magnitude for our attempt to define the term “magnitude” or see Wikipedia.

Variable Star.  A star is classified as a variable star if its brightness at any wavelength or band-pass changes as a function of time. If you could measure it precisely enough, you would find that every star is variable at some level.  What do you expect for a rotating ball of plasma undergoing nuclear fusion?  But realistically most surveys can not detect variations in brightness less than a few percent. So most of the time you would say a variable star is one that changes in brightness by more than a few percent from one observation to the next.  Often you would quote the variability in magnitudes.  One magnitude of variability represents a change of about a factor of 2.5.  That’s pretty big.  Imagine what your day would be like if the Sun changed in brightness by that much.  But this level of variability and more is common among young stars and among giant stars, for example.  If a star’s name stars with two capital letters, like RR Tau, then it’s known to be variable star.  (Though there are plenty of variable stars that have escaped this designation.)

VIZIER. VIZIER is a web-based astronomical database that enables one to query over 13,000 astronomical data catalogs from refereed literature by astronomical position or target name.  The type of data which can be accessed via these catalogs include the brightness of the object at a wide range of wavelengths (x-ray to infrared), amongst other properties.

WISE. The Wide-field Infrared Survey Explorer (WISE) is a NASA infrared space-based telescope that was launched in 2009 to perform an all-sky survey at 4 infrared band-passes, 3.4 microns, 4.6 microns, 12 microns, and 22 microns.  The Disk Detective project is mining the WISE catalog to detect new protoplanetary and debris disks.  The WISE mission has a website at NASA and a website at Berkeley.

Young Stellar Object (YSO).  This is shorthand for any star that appears to be in the process of forming.  You can think of these as baby stars that usually aren’t too far from a molecular cloud, which is where new stars form.  They can have jets, large disks, and can have variable luminosity as they accrete gas and dust on their surfaces.  YSOs can be  classified according to their Spectral Energy Distributions into Class 0, Class I, Class II and Class III objects. Also included in this group are transitional disks and “pre-transitional” disks and other kinds of interesting critters. See also Pre-Main Sequence Object.

A Dwarfs and K Giants

A list of 102 interesting objects that you helped pick for follow up (let us call them Disk Detective Objects of Interest, or DDOIs) shows that many of the stars with disks we locate will be A dwarfs or K giant stars. We don’t yet know all the spectral types of the DDOI stars precisely, but you can see the distribution of the types we do know in the figure below. The peaks correspond to A dwarfs and K giants.

Distribution of DDOIs according to spectral type. The two peaks at AV and K show that most stars hosting disks in our list are stars of type A and K that are about twice as massive as our Sun.

Distribution of DDOIs according to spectral type. The two peaks at AV and K show that most stars hosting disks in our list are stars of type A and K that are about twice as massive as our Sun.

So what are A dwarfs and K giants? “A” dwarfs are very hot, fast spinning and blue stars that are younger and brighter than “G” stars such as our Sun. The bright stars Sirius and Vega are some well known A dwarfs. Many of the best studied debris disks are around A dwarfs.

What are these “K giants”? K giants and A dwarfs are two sides of the same coin.  Let’s talk a bit about the life cycle of a typical star.

Most ordinary stars like our Sun burn hydrogen fuel for many millions of years. Once all the hydrogen is used up however, the star balloons in size and becomes a red giant. In the far future when our own Sun becomes a red giant, it will become so big that it will swallow up Mercury, Venus and possibly the Earth. Giants also tend to steadily lose a lot of their own mass all the time. This is because hot winds are blowing off the gas that is part of the star. (This hot gas is tricky because it might be mistaken for a dusty disk)

K giants are former A stars that have evolved for hundreds of millions of years. Like the sun, they have burned through their hydrogen, and ballooned up in size. Both A and K stars are about twice as massive as our Sun.

image02

Left: Artist’s impression of Sirius, and A dwarf. Credit: NASA, ESA, G. Bacon

K giants are also really interesting because Jupiter-sized exoplanets orbiting these old, giant stars have been found to be more common than Jupiter-sized exoplanets orbiting less massive stars that are still on the main sequence. These exoplanets around K giants have been found by the popular radial velocity (Doppler shift) method.

Also, some of these K giants have debris disks, sometimes even dustier than their younger counterparts. This is surprising, because giants are very bright and light from the star exerts radiation pressure on small dust particles that ought to blow the dust away, or cause them to slow down and spiral into the star and be swallowed up.

So where is the dust around these K giants coming from? Nobody really knows yet, but there are several hypotheses. One is that dust is coming from the star itself. Another is that the dust is in fact interstellar dust in our galaxy. A third is that giants are breaking up more comets. Whatever the cause, we have a lot of K giants in our list of DDOIs that potentially have dusty disks–so once we can follow these up with telescopes we will be able to help solve this mystery.

Dawoon Jung (@dirkpitt2050) is a graduate student at the International Space University currently at NASA Goddard Space Flight Center doing a summer internship with the Disk Detective team. He was born in Korea, and is interested in exoplanets and space flight.

​Herschel image of κ Coronae Borealis 31.1 parsecs away. This K giant is about twice as massive as our Sun. The red regions correspond to dust orbiting the star. Interestingly, this star also hosts at least one exoplanet with a mass of about 2 Jupiters. Credit: Bonsor et al. 2013.

​Herschel image of κ Coronae Borealis 31.1 parsecs away. This K giant is about twice as massive as our Sun. The red regions correspond to dust orbiting the star. Interestingly, this star also hosts at least one exoplanet with a mass of about 2 Jupiters. Credit: Bonsor et al. 2013.

Tutorial Video

If you’d like some quick tips about how to get started on Disk Detective, take a peek at this little video (below). I’m proud to say that this tutorial is the work of Disk Detective users, who wanted to help new users enjoy the site, and fill in some of the gaps in the other online instructions.

The concept for the video emerged from a round of discussion with Tadeáš Černohous, Phillip E. Griffith Sr., Doug Niergarth, Art Piipuu, Fernanda Piñeiro, John Reed, and Karl Wraight, Lily Lau and Hugo Durantini Luca.  Lily Lau and Hugo Durantini Luca provided the footage and a draft of the script. I had the honor of narrating, and Scott Wiessenger, a video producer at NASA Goddard Space Flight Center, kindly edited it all together.

For official versions of the video in various formats, see this page at the Goddard Science Visualization Studio.

For more advance tips on how to use Disk Detective, you might enjoy these blog posts.  And of course you can always contact us on the “Talk” network.

Best,

Marc Kuchner

Disk Detective–in Chinese!

We’re excited to announce that Disk Detective has been translated into Mandarin Chinese–both simplified and traditional character fonts! Many thanks to Ruobing Dong at the University of California, Berkeley Astronomy Department and Mei-Yin Chou at Academia Sinica’s Institute of Astronomy & Astrophysics (ASIAA) for the translation work and to Chris Snyder at Zooniverse for the technical work.

Here is a brief description of Disk Detective in traditional character Chinese and then followed in English:

類似地球的行星是在圍繞著年輕恆星的氣體、塵埃、岩石和冰塊所構成的盤中形成。我們需要你的幫忙來找出更多這種孕育行星的盤,這樣我們才能找 到系外行星且更加了解它們如何成長。

為了找到這些盤,我們結合了數十萬張來自美國太空總署(NASA)的廣域紅外線巡天探測(WISE)任務的影像。已經有很多科學家搜尋來自 WISE的資料並試著用電腦找出這些盤。然而這些盤容易跟星系、小行星、星際物質團塊和其他天體搞混,科學團隊檢視後發現必須用人眼來辨識這 些資料才行。

在尋盤偵探(DiskDetective.org) 中,有了你的協助,這些被辨識出來的盤將能用來建立一個最大的盤資料目錄。NASA的James Webb太空望遠鏡和其他望遠鏡將用這個目錄為主要目標來尋找系外行星。我們找到的這些盤將有助於了解太陽系的過去跟未來。

http://www.diskdetective.org/?lang=zh_tw

Planets like the Earth form within disks of gas, dust, rock and ice grains that surround young stars. We need your help to find more examples of these planet-forming disks so we can locate extrasolar planets and better understand how they grow and mature.

To find these disks, we’re combing through a catalog of hundreds of thousands of sources from NASA’s Wide-field Infrared Survey Explorer (WISE) mission. Many scientists have been searching through the data from the WISE space telescope to find disks using computers. But the disks are mixed in among galaxies, asteroids, clumps of interstellar matter, and other contaminants. And each team that has looked through the data has found that every source has to be verified by eye.

With your help, at Disk Detective.org we will produce a catalog of verified sources many times bigger than any other catalog. This catalog will yield key targets for NASA’s James Webb Space Telescope and other telescopes to search for exoplanets. The disks we find will help us understand the history and future of our solar system.

Marc Kuchner  and Meg Schwamb

 

 

Good News Everyone! 272,000 More Subjects

January 28 we launched DiskDetective with a first batch of about 32,000 sources to classify.  Of these, 20,000 have been in rotation at any given time.  That’s a lot of astronomical data–and a lot of flipbooks to look at.

Well, it completely shocked us when we heard in March that some folks were seeing repeats–meaning that they had already classified more than 20,000 subjects!  Now, we had always planned to have many more subjects than that in Disk Detective.  But at that point, we were still in the process of downloading the data from the NASA/IPAC Infrared Science Archive onto a hard drive on Marc’s living room carpet, a process that took about a month. So we weren’t ready to put any more data online to keep all our detectives detecting.

But now we are ready.  I’m excited to say that we’re adding about 272,000 more subjects to Disk Detective, a massive data blast that will probably keep us all busy until well into 2017.  The new subjects will start rotating in to everybody’s queue today, bit by bit.

Thank you for all your hard work that led us to this day!

Now, this next batch of data will be a bit different than the batch you’ve already been working on in two important ways. First of all, the first batch of data came mostly from the Galactic poles (To be precise, they came from regions with Galactic latitude  +50 to +90, +30 to +40, and -40 to -90.) The new data fill in the rest of the missing regions–right in the middle of the Milky Way (as illustrated crudely to the right). Where the new sources come from

Debris disks are located at all Galactic latitudes.  But most YSO disks are located in the Galactic plane, i.e. at Galactic latitudes less than about 30 degrees.  So as we dip into this new data, we’ll start seeing more YSO disks like Herbig Ae disks and T Tauri disks. We might even see some transitional disks: massive gas disks with big central holes, thought to be in partway between YSO disks and debris disks.

Also, as we look closer to the Galactic plane, the kinds of contamination will change.  The plane of the Milky Way is chock full of interstellar dust clouds, as the image on the right shows. Beware, some of those clouds may have patterns in them that mimic the appearance of our disk candidates!

Second of all, for this new batch of data, we’ve removed many of the fainter objects, specifically, all objects with J magnitude > 14.5.  (Remember, higher magnitudes mean fainter objects.) Here’s why.

The figure below shows the distribution of the J magnitudes of the sources with excess emission at 22 microns that WISE made really high quality images of (specifically ones from Southern Galactic latitudes, but that doesn’t matter).  The total distribution, shown by the black curve, has two peaks, one around J=9, the other around J=16.

What is the meaning of these two peaks?  Could it be two different kinds of sources?

The red and orange curves tell the rest of the story.  The red curve shows the numbers for just those sources close to the Galactic plane. The orange curve shows the numbers for the remainder of the sources–those far from the galactic plane.  Dividing the sources up in this manner shows that the second peak is mostly due to distant galaxies.

At low galactic latitude, dust from our Galaxy, the Milky Way, obscures most galaxies external to our own.  So we know that the objects shown by the red curve–most of the peak at J=9–are stars (and maybe stars with disks).  At high galactic latitude, the opposite is true.  The objects shown by the orange curve should be mostly galaxies. That’s the peak at J=16.

For now, we’d like to skip the objects that are mostly galaxies (orange curve) and concentrate on the objects that are mostly stars (red curve).  The orange and red curves cross at about J=14.5,  so we decided to put aside the objects with J > 14.5 for now. That means this new batch of data should have fewer galaxies in it than the old batch–and more of those delicious disks!
Jmag_distribution

What are we doing with the sources with J magnitude >14.5?  Don’t worry, we’ll be putting them to good use.  Our colleagues have suggested that hidden among those fainter sources could be Kardashev Type II and Type III civilizations. So once we’re done with this new batch of sources (roughly in 2017), we’ll start looking at the fainter objects–looking for signs of extraterrestrial intelligence.   In fact–you may have already spotted some in the first batch of data.  (They look just like debris disks and very red galaxies).  Stay tuned!

Follow-Up Observing Begins!

In our last blog post, we invited you to submit interesting targets to follow up with the Tillinghast 1.5m telescope at Mt. Hopkins this spring. Thank you to jessicamh, Gez Quiruga, arvintan, kmasterdo, silviug, wtaskew, cpitney, Pini2013, Ted91, Vinokurov, michiharu and everyone else who submitted targets!  Thanks to your help, we picked out 102 objects to follow up this spring.  The observing starts tomorrow night.

And guess what? We’ve got more follow-up observing planned for the fall semester, and also for the Southern hemisphere, with help from our new collaborators, Luciano Garcia and Mercedes Gomez from Observatorio Astronómico de Córdoba and Christoph Baranec from the University of Hawaii.

So we’re keeping that target submission form open.  From now on, whenever you find an interesting target, anywhere in the sky, feel free to submit it.

And now that we’ve been through this process, I can better explain how we decided what to follow up this time. This part of the blog post is going to be a bit technical–so feel free to skip it, or ask us for more info if you get tripped up by the jargon.

We started by searching SIMBAD and VizieR for information on each object, keeping the search radius to 0.2 arcminutes. These are the kinds of objects we most want to follow up:

Main sequence stars  (aka dwarfs)
Luminosity Class IV stars:  A IV, F IV, G IV, K IV, M IV.
A III, F III, G III and K III stars
T Tauri stars and Herbig Ae stars
white dwarfs
objects with distance < 200 parsecs
objects with proper motion > 30 milliarcsec/year
shell stars

We generally don’t want to follow up:

M giants
Cepheids
Be stars
galaxies, Active Galactic Nuclei
blends (i.e. two objects so close together that we can’t analyze them separately)
eclipsing binaries
O stars
supergiants

Also mixed in the lists of possible targets were:

binary stars
known disks
and plenty of objects where we can’t tell what it is

These objects went onto a “Maybe” list, to be followed-up as second priorities.

We could read some of this information from the SIMBAD spectral type. The quality of this information varies, and the SIMBAD spectral type includes a data quality letter (A,B,C,D, or E) where A is the best.  Since the purpose of this observing run is to weed out blends and to get more accurate spectral types, we figured it was OK to look at objects where the spectral type quality was poor. But we threw out objects classified in SIMBAD or VizieR as M giants, Cepheids, Be stars, galaxies, Active Galactic Nuclei, eclipsing binaries, O stars or supergiants.

The most common contaminants are M giants and supergiants.  We want to avoid those. But some M stars are main sequence stars (dwarfs). Like this one: AWI00003dm  Disks around these M dwarfs are rare and interesting and worth extra points! So we must be careful weeding out the M giants and supergiants.

M giants are sneaky!  They come with many different labels in SIMBAD and VizieR: Long Period Variables (LPVs), SR+L, Slow Irregular Variables, Miras, Semi-regular Variables, Semiregular pulsating Variables, Carbon stars.  All those are kinds of M giants/supergiants and they tend to make their own dust, so we can’t use dust around them as an indicator of a planetary system. We’re not following them up.

https://i0.wp.com/www.circumstellardisks.org/imgs/AUMic_krist05.jpg

M dwarf disks are exciting but rare. Here’s a Hubble picture of one around a star called AU Microscopii.

Sometimes you can spot an M giant even when there’s no known spectral type. For example, subtract the V magnitude from the K magnitude.  If V – K > 3.29, you’re looking at an M star.  Then, if a star has a measured distance of thousands of parsecs, you can bet it’s a giant or supergiant.  So we declared some objects to be M giants based on color and distance. A real M dwarf is so faint we can only see it if is much closer than 100 parsecs.

Here’s more information about how to guess a star’s spectral type based on its color:  http://www.stsci.edu/~inr/intrins.html

If you know you’re looking at an M star, another good clue that it’s a giant/supergiant is if it is highly variable (e.g. amplitude more than one magnitude).  So we looked up the variability amplitude for our targets in VizieR as well.

For an M star with no parallax measurement and no variability measurement, it can be hard to tell if you’re looking at a dwarf of giant or supergiant. So I put objects like that on the “maybe” list.

And finally–all the subjects on Disk Detective are preselected to have a certain degree of redness (we require the WISE 4 magnitude to be at most the WISE 1 magnitude – 0.25). But that’s not sufficient to find M star debris disks, since M stars are so cold, and therefore intrinsically red colored. We had to additionally weed out M stars with WISE 4 magnitude > WISE 1 magnitude + 1.0. (I know that sounds terribly confusing–it’s confusing because in the astronomical magnitude system, brighter objects have lower magnitudes. But adding this second criterion says that we are being more demanding when it comes to M stars in terms of how much brighter they need to be in the WISE 4 band than the WISE 1 band.)

Whew—that’s a lot of detail, I know. But now you can see why we try to weed out all those blends and multiples etc. using the handy animated flipbooks on the DiskDetective site before we start all the detailed research on each one.

Here are all the objects on our current version of the follow-up list for the Tillinghast 1.5 m for this spring, below (this list includes the maybes).  Thanks again for all your hard work.  And keep our fingers crossed for good weather at Mt. Hopkins!

Marc

Zooniverse ID
AWI0000bs0
AWI0000tjx
AWI0000gjb
AWI0000fye
AWI0000kg4
AWI0000ojv
AWI0000tz1
AWI0000u8s
AWI0000uj2
AWI0000uji
AWI0000w9x
AWI0000ibq
AWI0000v1z
AWI00006nk
AWI00000wz
AWI0000tgc
AWI00002ms
AWI0000cot
AWI0000nwt
AWI00002zo
AWI0000m2p
AWI0000ns8
AWI00004o8
AWI000050r
AWI0000hjr
AWI000048c
AWI00005uf
AWI00000o6
AWI00001l8
AWI00002yt
AWI0000hog
AWI0000kk6
AWI0000eg6
AWI000004g
AWI00007qu
AWI000001j
AWI00001q1
AWI00005xz
AWI00006bt
AWI00004qc
AWI00000zp
AWI0000kgo
AWI00007dp
AWI00000om
AWI00006dp
AWI0000149
AWI000011b
AWI0000l8w
AWI0000us7
AWI0000gz9
AWI000028h
AWI0000vk9
AWI0000jo8
AWI000015r
AWI00000au
AWI000066t
AWI00002xh
AWI00006kc
AWI0000632
AWI0000np1
AWI00002fw
AWI00006p0
AWI0000ajw
AWI00007i1
AWI000047d
AWI0000tpu
AWI0000qxd
AWI0000hat
AWI000055c
AWI0000wip
AWI00006b3
AWI0000tsh
AWI00002hx
AWI000054k
AWI00001sw
AWI0000r07
AWI0000t35
AWI0000a7e
AWI000019z
AWI0000s7e
AWI0000wqx
AWI00005x2
AWI000042e
AWI0000aoe
AWI00004ox
AWI00000lj
AWI00000my
AWI000034n
AWI00004c1
AWI00005ko
AWI00006hl
AWI00006nb
AWI00007fu
AWI00007ne
AWI0000c02
AWI0000l70
AWI0000s8t
AWI00006m2
AWI000072k
AWI0000qnj
AWI000016c

Send Your Favorite Targets!

Detectives,

You may recall that in February, we submitted our first follow-up observing proposal.  We asked for two nights of time on the FAST spectrograph on the Tillinghast 1.5m telescope at the Fred Lawrence Whipple Observatory.

Well, not only did the time allocation committee like our proposal.  They gave us more time than we asked for! Depending on the weather, it looks like we will have about four nights to follow up our favorite good candidates.

So now we need to make a new list of targets, and we need your help!

Please send in your suggestions using this online form. We’re looking for objects that are:

1) Good candidates in Disk Detective.

2) Mostly in the Northern hemisphere.  So make sure the declination is > -20 degrees.

3) Up at night during the months of May-July.  That means the Right Ascension of the object should be less than 25 degrees, or greater than 120 degrees.

4) Bright enough to see with this telescope.  That means V magnitude < 15.  You can find the V magnitude for some of the objects at SIMBAD through the Talk pages.  For other objects, you have to look in VizieR. Remember, when you search VizieR, change the search radius to 0.2 arcminutes, to match the WISE beam at 22 microns.

5) And while you’re looking in SIMBAD and VizieR, jot down the spectral type, parallax, the J magnitude, the proper motion, etc.

On this observing run, we will be collecting medium-resolution spectra of the targets, to check if they are indeed stars, and to get better measurements of their luminosity classes–whether they are on the main sequence or not. So if there is not much information in the literature about the spectral type, that’s OK.

But some targets will be clearly identified as giants, or supergiants, or Cepheids, Miras, Be stars, RR Lyrae stars, or Long Period Variables.  These kinds of stars all make their own dust, so finding a disk around them doesn’t indicate a planetary system. You can send those in if you want, but they won’t be our first priority this round.  For now, we’re mainly interested in dwarfs and subgiants (luminosity classes IV and V) and even white dwarfs, if you can find them.

Send in your new target suggestions–as many as you like–in by this Friday (April 11).  And if you can’t find any in time this week, don’t worry! We’ll be applying for more observing time later on.

Here’s the URL for that submission form: https://docs.google.com/forms/d/1DfmYSrg614osuLaUsac_a03dX-Bt6Ab2ep5SXC4XWHw/viewform

Good luck!

 

Best,

Marc

@marckuchner