When you find a good candidate at Disk Detective, it goes into our queue to be researched and often to be re-observed. Many of those good candidates that are in the Southern Hemisphere get re-observed from the CASLEO observatory in Argentina, where we split up their light with a spectrograph to find out what kinds of stars they are.
Disk Detective Hugo Durantini Luca lives in the city of Cordoba, Argentina, much closer to the CASLEO observatory than most of us on the Disk Detective science team, but still a long journey away from it. He traveled for more than eighteen hours across the country of Argentina to join a Disk Deective observing run. Hugo spent five days on the mountain with Luciano García (astronomer from Observatorio Astronomico de Cordoba) helping observe good candidates. He wrote down some memories from the trip to share with us. I think you’ll find them as inspiring and poetic as I did!
You can read about his experiences below, and even watch some short videos he took at the observatory:
Dentro de la Cúpula de CASLEO / Inside the CASLEO Dome
Afuera del Observatorio de CASLEO / Outside the CASLEO Observatory
Centro de Control de CASLEO / CASLEO Control Room
My Travel to CASLEO
by Hugo Durantini Luca
Reaching CASLEO requires a little patience. Even if you were to reach the city of San Juan by plane, you still have to endure traveling approximately 5 and half hours more to reach the observatory. The landscape is very interesting, especially if it’s your first time in the region, with the mountains presenting multiple colors and the sight of the Andes while you gradually approach to its foot.
After getting off the bus to San Juan, I was greeted almost immediately by Luciano García and we started our travel to the observatory after picking up some staff that also was going to the complex to start their work shifts. I don’t know if was because I just had made a 8 and a half hour trip, or if it was because of the landscape and the excitement, but the travel of almost 5 hours from the city to the complex felt pretty quick and we reached the place just in time for lunch.
After that, we checked in to our rooms and I was able to do a small tour to see with my own eyes the telescope along with the instrument what we were about to use: the REOSC Spectrograph. The sensation of seeing all the instruments and the control room in person was almost like going back to my childhood, even though I had previously checked all available information on the internet.
I must say that the first night was a bit hard, not only because at first we lost the first hour or so thanks to the clouds, but also because after we started the work and learned the basics of what we were about to do, fighting the urge to sleep and our biologic clocks was something that required a little technique.
To input the coordinates of the star that we wanted to observe and then to give the order to REOSC to initiate the exposure was a great privilege. I was assigned this task for the whole run. But even repeating this process over and over didn’t diminish the excitement of directly generating new data for our research.
Another amazing experience was to go outside of the telescope and be able to contemplate the Milky Way in a clean and clear sky. I saw details that are impossible to see from the city due to light pollution, treasures that the people that have never left the city or studied astronomy don’t know they are losing.
It was really fun and illuminating for me to participate in all the nights, to watch how the instrument behaved according to the magnitude of the stars. I learned how to add more or less time to obtain a good reading and how in some cases, there is no trick aside from perseverance. All this experience brought me closer to a better understanding of the work of an astronomer beyond all the commons fantasies that one can hold.
The second day was much easier than the first, at least in the sleep management department. Even if your body is still complaining about some things; one can feel how it adapts to the day to night change. The second night was when we ended doing most of our brightest stars because even if they can be a little difficult, there is less exposure time required. I also had the chance, thanks Luciano, to explore and visit a few sites close to the complex. The landscape and autumn colors, views almost like paintings, and the lonely roads added to the unforgettableness of the trip.
All the CASLEO staff that we had the opportunity to interact with were extremely kind and it was like being at home almost all the time. Even though we were just there four days, by the end, I felt like I had been there for a long time. The return trip was somewhat bittersweet. You miss home, but at the same time this experience has reinforced to the max my love for science and especially astronomy.
To pass days far away and entire nights collecting information can look like something disconnected from reality, but it’s actually the opposite. To gain consciousness of the scale of our Galaxy and our place in the universe is an experience that makes you humble, and being able to participate in building our knowledge and understanding of the universe fills me with a sense of obligation to others here in our own world.
Steven Silverberg from our science team just came back from South America where he went to observe some Disk Detective Objects of Interest with the DuPont telescope. Here’s his story.
We have a program to take high-resolution images in the near-infrared band (between the DSS “IR” band and 2MASS “K” band we use on the Disk Detective site) with the 2.5m DuPont telescope at Las Campañas Observatory, one of the premier observatories in the world. It’s similar to our follow-up program with Robo-AO; the images help us double check for background galaxies and stars that could be lurking very near to our disk candidates, so close to them that they wouldn’t appear in the data we already have. We have access to this telescope in Chile thanks to Johanna Teske, a member of our science team at the Carnegie Institution for Science. Because Johanna couldn’t go on the observing run this time, I went to South America. It was my first time outside the US–very exciting!
The first thing that struck me were the spectacular views. LCO is 2,380 meters (7,810 feet) up in the edge of the Andes. For someone who grew up in the part of Texas that doesn’t have mountains, it was rather incredible.
My first night there was spent shadowing an observer for the Carnegie Supernova Project, an ongoing campaign to fully characterize the behavior of supernovae in multiple bands. Unfortunately, most of this night was wind-ed out. DuPont has a firm wind speed limit of 35 miles per hour; anything above that, and the dome must close.
Most of DuPont’s controls are handled by computer. However, one last panel from the original control board is used for operating the lamps used for calibrating the detector (the dials next to the LCD readout). The rest of the panel has been superceded by computer, hence all the “Do Not Use” signs.
One upside to going nocturnal for telescope time: you’re awake for amazing sunrises and sunsets. In this case, morning twilight on the mountains to the west.
The most impressive feature of the observatory was the mountain on which the twin Magellan telescopes reside. These two telescopes, each 6.5 meters in diameter, loom over the observatory lodge. LCO will eventually (by 2025) be the site of the Giant Magellan Telescope, which (along with telescopes like JWST) could be used to image Disk Detective disks!
There are two other major telescopes at LCO currently: the Swope telescope (in the foreground) and DuPont (centered), where we conducted our observations. These are the two oldest telescopes on-site; the Swope went on-line in 1971, while DuPont came on-line in 1977.
Because of the timing of my visit (right around full moon), I was able to get some excellent images of moon-rise. This one was taken before my first night of observations, which (like the night prior) was mostly lost due to wind. However, we were able to get 19 objects imaged on night 1, despite losing several hours to wind.
The sunrises were absolutely beautiful while I was on-site. I enjoyed taking pictures of them. These are several different captures of the sunrise after night 1 of Disk Detective observations, taken from my room at the lodge.
This was the view looking south from the lodge. The road below is the road back down the mountain from the site. GMT will be built on one of the mountains down here, to the left of this shot.
The road from DuPont back to the lodge. As one might expect for a mountain in the Atacama desert, the local foliage was rather sparse. The same weather conditions that lead to this sparseness make LCO an amazing site for astronomy.
While on the mountain, I got to use a car reserved for DuPont observers. Having never driven on a mountain before, that was new and different…and a bit frightening. Especially driving down the road above at morning twilight, with limited visibility.
The actual DuPont 2.5-meter telescope. Rather than use a (rather heavy and difficult to maintain) tube to support the secondary mirror (at the top), this telescope uses a truss to support the secondary mirror. As you can gather, this telescope was rather huge.
To give you an idea of how big this telescope was/is, here’s a picture of just the base, with a nearby staircase for scale. The staircase went up about ten feet.
This was the sunset before my second night of observations, as taken from DuPont. The clarity of the sunset shows just how good the skies are at LCO, making it perfect for astronomy.
During my time on DuPont, I worked with two telescope operators. These telescope operators handled the movement of the telescope, taking coordinates I gave them and slewing the telescope to its correct position, as well as adjusting the focus. This freed me up to focus on the astronomy, and made sure that someone who knew what they were doing with this particular telescope (as opposed to me, who had never used it before) was making sure the telescope was operating correctly at all times.
Sunrise over Magellan. Sunrises were pretty cool here.
While at LCO, I was able to get a few pictures of the European Southern Observatory-La Silla, which is on the next mountain over–the observatory next door, as it were. In fact, La Silla is just down the road from LCO. Seeing La Silla (even from a distance) was rather cool to me, as my home institution (the University of Oklahoma) does ongoing disk research with telescopes there.
DuPont, now with an astronomer for scale, after the last night of observations. The telescope did very well, despite the cloud issues–we were able to image another 39 targets, bringing our total for the observing run to 98 targets imaged.
DuPont served us well on this run. The telescope worked very smoothly, all things considered, and we were able to collect data on ninety-eight Disk Detective Objects of Interest, which we’ll be analyzing soon. Once that’s done, we’ll let you know what all we found from what you found!
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.
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.
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.
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.
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
objects with distance < 200 parsecs
objects with proper motion > 30 milliarcsec/year
We generally don’t want to follow up:
galaxies, Active Galactic Nuclei
blends (i.e. two objects so close together that we can’t analyze them separately)
Also mixed in the lists of possible targets were:
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.
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!