Dr. Andrew Drake Interview

Andrew Drake is a Research Scientist with Caltech's CACR (Center for Advanced Computer Research) in California. His astronomical interests are varied, and include exoplanet discovery, microlensing of Machos and other baryonic dark matter, Supernovae/Hypernovae and mining large data sets. He is the principle investigator for the Catalina Real-time Transient Survey.

Because one of the byproducts of the CRTS is the discovery of numerous cataclysmic variables I thought it would be interesting to have him to tell us about the methods and goals of the CRTS team, and what they are doing with all the new science coming out of their survey.

Mike: Hi Andrew. Thanks for granting this interview. Let's start off with a description of the Catalina Real-time Transient Survey, the methodology, it's science goals, and then discuss what your group is doing and what you're learning. So first, what telescopes and instruments are used for CRTS?

Andrew: It is my pleasure. The Catalina Real-time Transient Survey (CRTS) currently uses data from the Catalina Sky Survey's (CSS) 0.7m Schmidt telescope. The CSS team hunts for Near Earth Objects (NEOs) while we hunt for other kinds of stationary optical transients.

Mike: What is the observing cadence and how much of the sky do you cover?

Andrew: The Schmidt has an eight square degree fov and covers the visible sky between -30 and +70 degrees.

However, we avoid the Galactic plane by 10 degrees because of crowding. About 1200 square degrees is observed four times on each of the 21 darkest nights per lunation, to V~20.

Mike: Your interest and the science you are going after seems to relate mostly to supernovae in general and then supernovae in faint galaxies, correct? What are you hoping to learn from the survey?

Andrew: Our interest is in optical transients of all kinds. However, we are particular interested in the rare kinds of transient phenomena that can only be found through synoptic surveys covering a very large area. Two particular types of transients that have become of interest since we started the survey, supernovae in faint galaxies, and hypernovae.

Mike: In order to study these supernovae you need a way to filter out all the other stuff you're not looking for, which includes asteroids, cataclysmic variables, other types of variables, image artifacts, etc. You have to be able to classify objects quickly and accurately. I imagine that is one of the bigger challenges in your work. How do you go about doing that?

Andrew: Filtering artifacts and asteroids is perhaps the most difficult part of the survey. Fortunately most asteroids are known to the depth of our observations and can be removed using the ephemeris files that the Minor Planet Center (MPC) distributes. Additional asteroids and artifacts can be removed checking for motion, or offsets, between images. Even so, there is a balance between missing some real transients with strict filtering or allowing some junk through with looser filtering. We have never tried to filter CVs because we know many people are interested in them, particularly when they are in outburst. To improve classification we follow-up almost everything we discover with the Palomar 60" and also make this data public. Our hope is to obtain fully automated classification network to replace the final classification which still must be done by a person (gathering all data sources, cross-checking and making a decision). We hope our future automated classification will enable rapid robotic follow-up of short timescale transients.

Mike: What results have you found so far in your supernovae studies?

Andrew: One surprise to us was that a large fraction of the supernova we find are in intrinsically very faint galaxies. This is not expected because there is much more stellar mass in large galaxies and nobody has seen this before. We believe the reason this has been missed in the past is that most searches for nearby supernovae follow only a few hundred very bright galaxies. The increased SN rate in faint galaxies appears to be mainly due to an extremely high star formation rate in some low mass dwarf galaxies. One particularly interesting SN we discovered was 2008fz.

Mike: What was so special about SN2008fz? Was this a hypernova? What is the difference between a supernova and a hypernova?

Andrew: SN2008fz was a type IIn supernova discovered by CRTS and appears to be the most energetic supernova ever discovered. Such bright supernovae are often called hypernovae and are proposed to be the result of either the collapse of a massive star like Eta Carinae or an extremely massive population III star. The exact origin of hypernovae is not yet clear as few have been discovered. They up to a few magnitudes brighter thanregular type Ia and type II SN and have also been linked to exceptionally bright gamma ray bursts.

Mike: Now you've developed some tools and resources for amateurs and others to use to follow up on newly discovered CVs from CRTS. Tell us about that.

Andrew: When we classify our detections place them on a number of web pages where we hope people will find and follow them. New bright CVs are among our most common discoveries, although we include known CV outbursts also. As with all our discoveries these are made public as quickly as possible. Our hope was that people would work with us on the discoveries or at least inform us that they are following CVs, as they do with supernovae. Unfortunately, we find that they are taken from the webpages and circulated to email lists where they are quickly renamed and followed and even published under that name. Nevertheless, we are continuing to openly publish the new CV discoveries.

Mike: You're also logging data collected serendipitously on known CVs. Is there a plan to share these observations with AAVSO or other researchers? Is there maybe a project here for the CV section, or perhaps the data mining section, to convert your data into a format that can be periodically entered into the AAVSO International Database?

Andrew: Yes, as we cover a large fraction of the sky every lunation we realized that the data would regularly cover thousands of CVs and other interesting variables. We thought it may be useful for us to provide up to date measurements for known interesting objects so that CV astronomers might follow-up those that that they deem interesting. We certainly hope that the AAVSO will ingest this data.

Mike: So what are the plans for the future? Are you going to expand the project? How long do you think you will continue?

Andrew: Soon we hope to start processing the data from two additional dedicated CSS telescopes that use the same camera setup. There are also plans to expand the fields of the existing telescopes by a large factor. Depending on funding we plan to continue for three more years. Part of our goal is to make all the past CSS data public so that everyone may perform their own searches for variables, etc., among the tens of terabytes of existing images and photometry.

Mike: Well, I wish you the best of luck. Let's do this again some time. You can bring us up to date on what has developed for you and your team, and it will give us an opportunity to thank you for all the interesting CVs you're going to discover for us in the meantime!

Andrew: You are most welcome.

Serendipty and Cataclysmic Variables

Cataclysmic variable star research has benefited from the, often accidental, discovery of CVs during the course of astronomers doing other research. This has led to a lot of license plate type names like RSXJ01234.45+2345.6, HS 1234+5678 and PG 1234+67. These are prefix based names that indicate the space satellite or ground survey that discovered the star. RSX means it was a ROSAT satellite x-ray source, HS stands for the Hamburg Quasar Survey, and PG means it was discovered by the Palomar Green Survey (also looking for quasars). For more information on this plethora of naming conventions see my article "What's In A Name?"

Serendipity comes into play because all of these previously mentioned examples are stars discovered by surveys looking for other types of objects. ROSAT was looking for x-ray sources on the sky and the Palomar and Hamburg surveys were looking for blue objects in their search for quasars. The most common way CVs are discovered from these population of objects is by going into outburst and revealing themselves as much brighter in new images compared to older images. Until recently, it would be safe to say half of all CVs were discovered by their telltale outbursts or optical variability when active or bright.

Today a paper was published on ArXiv describing a new CV, RAT J1943+1859, discovered while astronomers were looking for variable stars in the field of the globular cluster M71. RAT stands for RApid Temporal Survey, an experiment utilizing the Isaac Newton Telescope. Even though the astronomers were actually looking for variable stars this time, what they didn't expect to find were stars exhibiting quasi-periodic oscillations (QPOs), a little understood phenomena of cataclysmic variables, while the CVs are in quiescence (faint).

That is exactly what happened in this case. Astronomers found a periodic oscillation of about 0.3 magnitudes with a period of approximately 20 minutes. Observations taken later with another telescope revealed the object to be four magnitudes brighter than the first set of observations. They caught it in outburst! Further observations and spectroscopy suggest an orbital period of about 90 minutes, which means it is very likely to be a UGSU type dwarf nova at a distance of about 1.5 kiloparsecs. If this distance is accurate, RAT J1943+1859 is one of the most luminous sources observed by ROSAT.

So far, observations have measured the system at minimum around 20th magnitude, and in outburst approximately 16.5V. If it is a UGSU it will have superoutbursts somewhat brighter than this that will last longer, perhaps a couple weeks. This puts it right around the faint limit for 30cm amateur telescopes to study in outburst to determine its type, orbital period and superhump period if it goes into a superoutburst.

Even more exciting than the fact this might be another interesting system for amateurs to monitor, is the fact that RATS has several million light curves in their data that can now be searched for this same kind of behavior. These astronomers may have discovered a new way to discover CVs! This also has implications as more surveys like LSST and PanSTARRS are readying to come online in the near future. Scientists will be developing ways to sort out specific kinds of stars from the terabytes of data these surveys will create every night.

In that new era, amateurs will be needed more than ever to sift through the strange and unique discoveries these surveys stumble on while monitoring the cosmos every night in unprecendented detail.

RATS, QPOs, serendipity and discovery. It's a new age already.

Astronomical Acronyms

Acronyms, acronyms...doesn't anybody know how to spell any more? Every article or blog I read, every conference I attend, even watching the cable news channels, I am constantly bombarded with acronyms for everything. I rattle them off in conversation all the time without thinking, and yet I'm sure there are people listening, nodding their heads knowingly, who haven't got a clue what the heck I am talking about.

I do the same thing. My boss, a PhD astronomer, throws these things around as if they were real words and I should know what they are. I nod my head knowingly and scrape by as best I can until I have time to research them later. I usually spend about an hour or so investigating each set of mystery letters, divining the meaning of it all, so next time it comes up I can make an intelligent comment, or at least not stand there with a dumb look on my face.

This blog was inspired by recent discussions about all sky surveys, which naturally all have acronyms for names. My guess is that this will turn into a series of blogs on acronyms related to various aspects of astronomy. If you have a suggestion, leave it in the comments section, please.

Without further ado, here are Simointerpretations of popular acronyms related to astronomical surveys.

2MASS The Two Micron All Sky Survey is an all sky survey in the near infrared performed by twin 1.3 meter telescopes, one at Whipple Observatory in Arizona and the other at Cerro Tololo Inter-American Observatory in Chile. The University of Massachusetts lead this project. They were responsible for developing the cameras, telescopes and on-site computing systems. The project was funded by NASA and the National Science Foundation. It ran from 1997 to completion in 2001. The resulting 2MASS All Sky Catalog was released in 2003.

The reason it isn't called TMASS is because there was already an all sky survey in the infrared named TMASS done in the 1960's. 2MASS canvassed the sky with about 50,000 times the sensitivity of TMASS. They were able to study galaxies and objects typically hidden from view in optical wavelengths by dust in our galaxy and survey the sky for brown dwarfs and other oddball objects that emit most of their feeble light in the infrared.

To summarize, 2MASS, run by U Mass, funded by NASA and NSF, replaced TMASS by surveying the sky with twin 1.3M telescopes in the near-IR from Mt. Hopkins and CTIO.
Sorry, I couldn't resist.

ASAS The All Sky Automated Survey is an ongoing effort. Four small telescopes in Chile survey the southern sky, from +28 degrees to the south pole, down to about 14th magnitude every clear night in V and I bands. ASAS North, covering the northern sky, should be online soon.

HAT The HAT acronym stands for Hungarian-made Automated Telescope , because it was developed by a small group of Hungarians who met through the Hungarian Astronomical Association (HAA) back in 1999. The scientific goal of the project is to detect and characterize extrasolar planets and bright variable stars. The HAT and ASAS telescopes are very similar in size and appearance, since both are the brainchild of Bohdan Paczynski. The telescope pictured here is the HAT model.

LINEAR Lincoln Near Earth Asteroid Research is a Massachusetts Institute of Technology (MIT) Lincoln Laboratory program devoted to detecting and cataloging Near Earth Objects (NEOs) that threaten Earth. As of the end of 2007, LINEAR had discovered 225,957 asteroids. The twin telescopes located at the White Sands Missile Range in New Mexico also manage to serendipitously discover their fair share of comets, 236 at the end of 2007, which has discouraged many amateur comet hunters. These comets all get the unfortunate, unromantic name of comet LINEAR.

LSST The Large Synoptic Survey Telescope isn't even online yet, but I hear news about it and its development every week. This survey will utilize an 8.4 meter telescope with a 10 square degree field of view to survey the entire night sky visible from Chile once every three nights. The LSST camera will be 1.6 by 3 meters and weigh 2800 kilograms! It will just sit there night after night, cooled to -100C, endlessly shooting 15 second exposures, tracking objects that change or move on rapid timescales, like supernovae, near-Earth asteroids, and as yet to be discovered Kuiper Belt Objects. It will also be used to study faint, distant galaxies and dark matter.

NEAT Near Earth Asteroid Tracking, another program designed to detect and track NEOs, both asteroids and comets. This survey uses two 48" telescopes, one in Hawaii and one on California.

NSVS The Northern Sky Variability Survey is approximately one years worth of data from the ROTSE experiment (yet ANOTHER survey acronym!) used to detect and classify variable stars in the northern sky.

OGLE The Optical Gravitational Lensing Experiment project's main science goal was to search for dark matter using microlensing phenomena. The cameras basically stare at the Large and Small Magellanic Clouds and the galactic bulge, because that's where the most background stars appear from Earth. This experiment has to be considered a smashing success as they have not only detected microlensing phenomena, but discovered thousands of variable stars, dozens of exoplanetary transits, performed precision astrometry and photometry on thousands of stars, and mapped interstellar extinction from dust in our galaxy. By the way, this experiment was also proposed by Bohdan Paczynski. I guess you'd have to call him the father of astronomical surveys, eh?

PanStarrs Sounds like a Howard Hughes space enterprise, doesn't it? This project needs an acronym, because it has way too long a name- Panoramic Survey Telescope & Rapid Response System.

The immediate science goal of Pan-STARRS is to discover and characterize Earth-approaching objects, both asteroids and comets, that might pose a danger to our planet. Sound familiar? Musta' been a whole pot of money available for these type surveys once they became politically correct. "Hey, I see an asteroid. Send me money!"

The huge volume of images produced by this system will also provide valuable data for many other kinds of scientific programs. I hear it referenced in regards to all the transient and variable star data it will produce on a regular basis. The challenge for variable star researchers will be to scan through all the data and find those few interesting objects worthy of follow up observation programs. This scope and LSST are supposed to provide nightly alerts of transient phenomena, as well as terabytes of data. We need to get more AAVSO observers ready, and we need them now!

PQ -Palomar Quest Now here is an ongoing survey that I confess I hadn't heard abut until my boss mentioned it in passing. This survey uses the 48" Samuel Oschin telescope at Mt. Palomar to study Quasi-Stellar Objects (QSO), supernovae, variable stars, galactic structure and stellar astrophysics. Significantly, this is the first major digital sky survey designed and implemented in the Virtual Observatory environment. Now there's an interesting topic loaded with acronyms (NVO). Perhaps installment number two in this series.
I just love this picture of Hubble at the finder scope of the 48", conveniently pointed for him to pose at the eyepiece as if he actually guided long exposures with a pipe in his mouth.

SDSS The Sloan Digital Sky Survey is the "most ambitious astronomical survey ever undertaken. When completed, it will provide detailed optical images covering more than a quarter of the sky, and a 3-dimensional map of about a million galaxies and quasars. As the survey progresses, the data are released to the scientific community and the general public in annual increments."

This 2.5 meter telescope system is straight out of science fiction. The dual spectrographs are fed by fiber optic cables inserted through pre-drilled precision plates in order to measure up to 600 galaxies or stars per exposure. The list of discoveries and science accomplished thus far with SDSS is impressive.

And last but not least...
UCAC Two acronyms embedded in an acronym! USNO CCD Astrograph Catalog. USNO is the US Naval Observatory and CCD is Charged Coupled Device. Egads, layers upon layers of acronyms within acronyms. This is an all sky astrometric (positional) survey measuring the position and proper motion of stars to a very high degree of accuracy. The final catalog should be released in 2008.

If you haven't had enough yet, here is a link to a more extensive, although not necessarily current, listing of astronomical surveys, most with acronyms for names.

There now, don't you feel smart?
The next time someone mentions one of these surveys you'll know what they are talking about. Then you can look around to see who is nodding their head knowingly with that blank expression on their face, and have pity.