PHYS 141 Secrets of the Universe - Fall 2014

Course materials are starting to appear on Moodle. The textbook is Kirkpatrick and Francis, 7th ed.

Spitzer Space Telescope IRAC, IRS, and MIPS SED data for the 12 micron Seyfert Sample

I published a paper in 2010 presenting my Spitzer Space Telescope observations of the 12 micron Seyfert Galaxy sample. The paper includes some original data processing to optimize signal-to-noise and reduce artifacts. 

I'm occasionally asked for the data, which I happily share. The easiest way to get to the processed data is via ResearchGate. The spectra can be found at this link, and IRAC images can be found at this link.

Long-Slit Reduction in Python (pt. 2)

Some other projects have taken priority, and I haven't had time to complete my Python data reduction experiment. For anyone interested in trying Python for FITS data reduction, I've placed my incomplete reduction script at this link.

The script includes basic processing steps, including,

• Processing darks and flats,
• Applying dark and flat correction to image data (for a single image),
• Identifying the location of bright lines on arc-lamp images, tracing them along the spatial axis, and applying an interpolation to rectify an image along the wavelength axis. 

What's missing?

• I haven't calculated a wavelength calibration solution based on arc lamp observations.
• I haven't rectified images along the spatial axis.

OH maser detection using WIDAR on the Jansky VLA

OH (hydroxyl) maser galaxies are argued to occur in young quasars. OH masers appear as the quasar heats the surrounding molecular gas.

Masers are the radio wave equivalent of lasers, and they occur naturally in molecules with metastable energy levels; water vapor also produces natural maser emission.

OH masers commonly occur in interacting galaxies, and so it has been difficult to identify unambiguously which of the galaxies is the maser source. In addition, many of the early claims of OH maser detection were never confirmed, or the discovery spectrum was never published.

I'm involved in a project to use the Jansky VLA to observe a sample of OH maser galaxies. The new WIDAR correlator allows us to search a wider range of the radio spectrum. The OH molecule has four spectral lines in the spectral window we selected, although only two of the lines show maser emission strong enough to detect.

The goals of this project are to confirm the presence of OH maser emission and to determine the location of the masers to ~ 1 arcsecond accuracy (1 arcsecond = 1/3600th of a degree). This is my first time using the upgraded VLA, and the spectrum shown above represents the first detection from this project. The maser appears as a pair of closely spaced peaks in the spectrum. For reference, this OH maser galaxy is located at a distance of roughly 3.2 billion light years.

Toward Long-Slit Data Reduction in Python

I recently collected a bunch of long-slit spectroscopy data at the Apache Point Observatory 3.5m telescope. Now, it's been about 20 yrs since I've reduced a long-slit spectrum. I wasn't keen to re-learn IRAF, and so I thought I'd give it a try in Python. I've managed to get as far as correcting the distortion of the wavelength grid based on observations of neon arc lines. The correction is subtle: essentially, in the raw image, an emission line gently curves so that an image column does not map uniquely to a specific wavelength. The correction removes this curvature.

This wavelength grid correction makes sky subtraction a lot easier, and my first results are shown in the figure below. The top panel is a raw spectrum of an active galaxy; actually, if you look closely, you'll see spectra of two galaxies whose nuclei fell within the slit. The spectrum is dominated by sky glow (bright vertical lines). The bottom panel shows the image after the wavelength grid correction, and the sky glow has been subtracted by interpolating over the source. The quality of the sky subtraction has been affected by cosmic ray hits, but it's a good start. To be clear: all work was done in Python with no help from IRAF!

I've been meaning to post a spectrum from the APO observing run, but fighting the snow has kept me busy. Instead, here's an undoctored smartphone photo of icicles illuminated by moonlight.

I just returned from the Apache Point Observatory

I was using the Dual Imaging Spectrograph on the APO 3.5 m, shown here on an unfortunately cloudy evening. On a clearer night, I managed to collect some excellent observations of a sample of active galactic nuclei.

Sunset at the Apache Point Observatory

You can see the silhouette of the Sloan Digital Sky Survey (SDSS) telescope to the left, and the lights of Las Cruces, NM in the distance. Handheld smartphone picture with blurring effects provided by too much coffee.

NGC 6418 Reverberation: The Poster

I just learned that Michael Richmond has made Billy Vasquez' AAS poster available here.

A syllabus appears

Astrophysics students: a syllabus has appeared for ASTR/PHYS 301 on moodle.bucknell.edu. There will be minor changes between now and the end of the week, but more importantly I haven't figured own when I should schedule office hours yet. We'll talk about the best time for office hours during our first class.

Let me know if you cannot access the Moodle page; it's possible that I forgot to set some hidden, virtual toggle.

Right now the Moodle page is available only to students registered. This restriction is necessary to protect fair-use, copyrighted material. I'm happy to register guests who might be interested; please e-mail a request!

Reverberation Mapping of the Dusty Torus of AGN NGC 6418

On Tuesday Jan 7, +Billy Vazquez (RIT) presented his monitoring study of NGC 6418 at the +American Astronomical Society meeting in Washington DC. I encourage everyone to hop in a time machine and go visit his poster.

It's a neat result. NGC 6418 is a relatively low luminosity active galaxy, which means that it harbors an accretion disk that gradually feeds a supermassive black hole. We monitored the accretion disk with visible light observations, and we simultaneously monitored the surrounding dusty torus with +Spitzer Space Telescope infrared observations. The infrared measurements have a relatively rapid cadence of 3 days between observations (for my part, I was responsible for setting up these infrared observations).

Billy found that the infrared signal lags the visible light signal by 30-40 days, which implies that the size of the dusty region is around 30-40 light days, or about 200 times the semi-major axis of Neptune's orbit in our own solar system. Since NGC 6418 is so far away, we wouldn't be able to take a clear picture of the dusty region, although infrared interferometry might have a shot at confirming the size. The apparent size of the dusty region is roughly equivalent to a penny viewed from a distance of one earth diameter.

Teaching Schedule, Spring 2014

ASTR/PHYS 301: Astrophysics. My current understanding is that the class runs MWF 11 - 11:50 AM. The textbook is Carroll & Ostlie, An Introduction to Modern Astrophysics, 2nd Edition (ISBN 0-8053-0402-9). It's the big orange book.