The Astronomer's Day On

Me on Mauna Kea (HI), during an observing run last August.
Those aren't the telescopes I was working with - the
SMA is an array of 8 radio dishes, whereas these are all
optical telescopes near the top of the mountain!

As I said in my introductory post, I am an Astronomy PhD student, studying at Columbia University. While the main focus of this blog is what I do when NOT at work, astronomy is a very important part of my life. Last week, I had a thesis committee review: every six months (or so), the panel that will eventually be deciding if I get a PhD meets, and I give an overview of what I've been doing, and what I plan to do. This is all designed to keep my thesis ON TRACK, make sure I'm not floundering, and to give me advice on what they think I need to work on, or keep doing right. So, having just ruminated on my research, where it's going, and what my accomplishments are to prepare for this meeting, it seemed an appropriate time to introduce readers of this blog to my research.

In a word, I study novae. Novae can occur in binary systems where a compact star (most often a white dwarf) accretes mass from its companion. When enough matter builds up on the surface of the star and some critical mass is reached, it triggers a thermonuclear reaction which blows off material from the white dwarf as a shell of plasma. This material is quite hot and luminous, so naturally at this point you will see the star brighten - hence the name, "nova", which means "new star." Depending on the type of nova, this material will brighten and fade on the order of days to weeks to a few months - in the OPTICAL range. However, my research focuses on the RADIO light curves of novae, and how they evolve over time. In the radio regime, the time it takes for the lightcurve to rise and fall is usually on the order of months to years.

A lot of my work is based on the fact that different frequencies of light travel through plasma differently (like X-rays travel through your hand, making it possible to image bones, but you can't see through your hand in visible light). Therefore, if you look at the plasma ejected from a nova in two different frequencies, you'll get two separate brightnesses. So you can watch a nova in multiple frequencies and watch how it changes in each one, put it all together, and using some simple models and assumptions, make estimates about various properties of the ejecta (and thus the star and explosion as well). One of the things I really like about novae is that they occur on a time scale that we can NOTICE and KEEP TRACK OF. A new nova can go off at any time, and people all converge on it at once. You can clearly see the time evolution of these objects, and have a list of novae which are doing interesting things.

 But... sometimes the models don't quite work. Our assumptions are too broad, or there is some extra factor we overlook, or we get an answer which flies in the face of current nova theory. One of these issues is going to be the basis of my thesis: we're finding too much mass. Based on standard nova theory, we can estimate how much mass should be ejected in a nova shell. But when we do our model fits with observations, we seem to get masses over an order of magnitude (ie 10x) greater than what we expect. So is the problem with theory, or with our model fit assumptions? We've been making more and more detailed observations of novae, and we're still getting these large masses, even when taking in some additional factors in our model fit - because you can only stretch parameters so far and still keep your assumptions reasonable.

One of the assumptions we generally make in our models of novae is that the material ejected is spherically symmetric. Now, we KNOW that isn't true - nova ejecta is known to have clumps, or jets, or other asymmetries - but its a useful first-order approximation to make. So I'm also interested in jets and outflows in general, and what they imply about the system. Jets appear on multiple size scales in the universe: they can appear in outflowing systems from white dwarves to active galactic nuclei. So, in addition to novae, I have interest in other systems with varying brightness due to accretion, with outflows - like cataclysmic variables in general (where variation is due to accretion between two stars), and symbiotic stars (white dwarf/red giant binary system). I also have a fondness for neutron stars, though I don't really study them specifically at the moment. So really, binaries, jets, and compact stars in general hold my interest!

Some of the VLA telescopes
(in it's SMALLEST configuration)

I'm working with a collaborative group (the e-Nova project) looking at a number of different novae in radio, optical, and X-ray. The majority of our observations come from the Karl G. Jansky Very Large Array near Socorro, New Mexico.  This is an array of 27 individual antenna, working together as one (very large) radio telescope. I've been out there three times; however, these have generally been to learn how to do radio data reduction and analysis, not for observations themselves. When you get time on the VLA, you can input your operating instructions in the online system, and the operators out in New Mexico take care of the observing for you. The only observing I've done personally has been one trip out to MDM at Kitt Peak, AZ, two years ago, and one trip last August to the Sub Milli-meter Array (SMA) on Mauna Kea, Hawaii. The first of those trips was with a class on observational astronomy, where students got sent to the telescope (of which Columbia owns a share) to get experience with optical observing. The second, however, was directly related to my research: in order to obtain time on the SMA, you are required to send out an observer for a week to assist the local operators. So, when we wanted time for high-frequency radio observations of a few young novae, I got tapped to go. It was a pretty awesome experience... though sitting for a control room over a long night actually gets rather dull after a while.

Anyway, my collaboration has recently submitted two papers on which I'm a co-author. They are still undergoing the referee process, so they're not "published" yet and will undoubtedly change a bit before final publication, but they've been listed on the Astro-ph archives. I'm 9th and 10th author on these - it's a large collaboration - so I didn't actually do much of the writing, my contributions were more on the data side, as well as in editing and general discussion. But if you are interested in a bit more technical detail about what I've been working on, you can find those papers here.