2014 IPAC Visiting Graduate Fellowship

Program Description

The Infrared Processing and Analysis Center (IPAC) at Caltech announces the availability of six-month graduate student fellowships. The program is designed to allow students from other U.S. or international institutions to visit IPAC-Caltech and perform astronomical research in close association with an IPAC scientist. Eligible applicants are expected to have completed preliminary course work in their graduate program and be available for research during the period of the award. Funding from IPAC will be provided for a 6-month period via monthly stipends, plus relocation expenses. Several students are expected to be accepted each year, subject to the availability of funding. Students are expected to be at IPAC during the duration of the Fellowship, nominally January to July, with some flexibility on the starting and ending dates.

Description of Research Projects

Found! M dwarf Debris Disks

Advisor: Peter Plavchan

Thanks to Kepler, M dwarfs are now known to have small planets, but how they form presents a puzzle. One way to identify planet formation is through their infrared "excess" during the planet-building phase of a young star's life. Young stars can appear brighter than expected due to dust grains around the star absorbing visible light and re-radiating it in the mid-infrared. This "debris disk" of dust is created from the collisions of planetesimals like comets and asteroids. Previous observations of young stars have shown that debris disks are common around AFGK stars, up to 33% for A stars. For M dwarfs, however, debris disks are extremely rare. For this project, Dr. Peter Plavchan has compiled an extensive collection of Spitzer Space Telescope MIPS observations of young and nearby M dwarfs. New Spectral Energy Distribution fits need to be derived by adding the WISE all sky photometry. We have identified new M dwarf debris disks, and the visiting grad student would take the lead on completing this analysis and writing it up for publication. Familiarity with scripted languages (Perl, Python) in a unix-like environment is preferred.

Precision Near-Infrared Radial Velocity Exoplanet Survey

Advisor: Peter Plavchan

We are pioneering new instrumentation techniques for precision radial velocities in the near-infrared. Precise radial velocity measurements are used to identify exoplanets around other stars. By going to the near-infrared, we can survey younger stars, lower mass stars, and mitigate the wavelength dependent radial velocity "jitter" noise from stellar activity. However, precise techniques for wavelength calibration and illumination stabilization are lacking for the near-infrared. Current efforts are limited to ~50-100 m/s precision using telluric absorption lines for calibration. Dr. Peter Plavchan has built an absorption gas cell, and a fiber scrambler to improve the precision obtainable in the near-infrared. We have demonstrated a 7 m/s inter-night radial velocity precision for bright sources. We have put together a pipeline to reduce high resolution spectra and extract radial velocities, and we have put together a set of observations from a pilot survey. The student would lead the application of this pipeline to our survey data, help continue the survey and follow-up observations, and write up the results for publication. Experience with spectroscopy, Matlab and IDL preferred.

Exploring the Disks around the Nearest Carbon Dwarfs

Advisor: Patrick Lowrance

Carbon dwarfs are currently thought to be a low mass star with an accretion disk supplied by an unseen white dwarf companion during its evolution. Current understanding of the formation and evolution of carbon dwarfs is limited by the small number of objects and observations. We currently have observations of a several of the nearest carbon dwarfs from 1 to 160um using 2MASS, Spitzer IRAC, and Herschel PACS to detect the proposed residual circumstellar disk. The closer distance will enhance the detectability of the disk, and thus the opportunity afforded by this program to add observational proof and exploration is valuable and ground breaking. This program can provide the spectral range and sensitivity to gain the observational understanding of the cold circumstellar disk and dissipation timescales around evolved stars which placing carbon in our ISM− a major building block of life as we know it. We are looking for a student to analyze the photometry from these different infrared instruments and compare with current models to determine parameters of these disks. Experience with infrared data and photometry would be preferred.

Local Benchmarks for Cosmic Evolution of Major-Merger Pairs - A Multi-band Study of SFR, Dust and Gas Content

Advisor: Kevin Xu

In the local universe, major mergers of galaxies of nearly equal mass trigger the most extreme starbursts (ULIRGs) and bright AGNs. It has been intensely debated whether there were much more mergers in the earlier universe, and whether mergers play dominant roles in the cosmic evolution of galaxies (mass growth, SFR quenching, etc). We are carrying out a multi-band study for a complete sample of 88 local star-forming major-merger pairs (median redshift 0.04), exploiting data obtained by our own observations using Herschel (dust emission in FIR/sub-mm), IRAM (molecular emission in mm) and GBT (HI emission in radio) and archive data (SDSS, GALEX, WISE, etc). The goal is to set the local benchmarks for the cosmic evolution of the SFR-to-gas relation (the Kennicutt-Schmidt law) for major-merger pairs, complementing a study on the K-S law for high-z mergers in the COSMOS field.

Search for SNe in Extreme Star-Forming Galaxies using the Palomar Transient Factory

Advisor: Jason Surace

Extreme star-forming galaxies are predicted to have very high supernova rates, typically much greater than one per year. The most extreme star-forming galaxies in the local universe are "luminous infrared galaxies" or LIRGs. These objects have been intensely studied by our group at IPAC, most recently as part of the GOALS project (Great Observatories All-sky LIRG Survey). IPAC is also a partner in the Palomar Transient Factory, a multi-year optical synoptic sky survey which in the course of mapping the sky has also imaged all of the northern hemisphere GOALS objects many tens of times over the course of the last five years. In this project difference imaging will be used to search for optical transients in the LIRGs consistent with SNe. The SNe rate will be compared with that expected from the amount of optically detected star formation seen in HST uv/optical/near-IR imaging of the same targets.

Characterization of Optical AGN Variability with the Palomar Transient Factory

Advisor: Jason Surace

The Palomar Transient Factory (PTF) is a synoptic optical sky survey executing on the Palomar 48-inch Oschin-Schmidt telescope. The telescope surveys nearly the entire north sky above the galactic plane with a short cadence from hours to weeks and a longer time period of several years. Although not specifically targeted, large numbers of AGN are coincidentally imaged, allowing a wide variety of time domain studies. In this project we will be examining the variability power spectrum of the various flavors of the AGN zoo. This will also provide the student experience in working with large time-domain databases and characterization of time-domain data with uneven cadencing. This may also include studies of optical vs. mid-IR AGN variability in the IRAC Dark Field, a synoptic survey location observed by both Spitzer and PTF.

The Herschel EDGE-on galaxy Survey (HEDGES): Investigating dust Processing in Galaxy Halos

Advisor: Eric Murphy

The study of edge-on spiral galaxies provides a dimension to our understanding of galaxy structure and evolution unobtainable in any other way. In particular, observationally characterizing the role of feedback processes resulting from the accretion, expulsion, and/or cycling of material between galaxy halos and disks is best carried out for such objects. Gaseous halos are both the depository of galaxy feedback processes (e.g., from AGN and supernovae), and the interface between the disk's interstellar medium (ISM) and the intergalactic medium, through which infall, required for lasting star formation in disks, occurs. To date, we have a fairly good picture of how warm and hot ionized gas is distributed in halos, and a rapidly improving picture for the HI, however the distribution of dust in halos, and their role in dust evolution, remain highly uncertain. Specifically, there are a number of outstanding questions regarding the physical processes governing the interchange of disk/halo material such as: (1) How does halo dust content relate to disk star formation activity? (2) What are the physical characteristics of halo dust (i.e., temperature(s), mass, emissivity, PAH mass fraction, and what does their variation with height from the plane tell us about grain modification by the energetic processes responsible for disk-halo cycling? (3) What can dust and radio continuum halos tell us about transport effects that are important for understanding the far-infrared (FIR)--Radio correlation? (4) How does the distribution of halo dust compare to that of other gas tracers, and hence what can we learn about how such dust is associated with various gas phases?

To investigate these outstanding questions we have acquired deep Herschel imaging with PACS and SPIRE to measure variations in their FIR spectral energy distribution (SED) as a function of disk height and energetics. Using these new Herschel data, we will be able to properly sample the peak of the halo dust SEDs (i.e., 6 bands between 70-500um) across many resolution elements, allowing for the first time the ability to map and characterize the distribution and evolution of halo dust (warm and cold components) for a sample of energetically diverse edge-on spirals.

Galaxy evolution along a cosmic filament

Advisor: Dario Fadda

This project will use recently released WISE data in conjunction with archival GALEX and SDSS data to study how the star formation rate of galaxies is affected by the environment along the filament connecting the Coma cluster to the A1367 cluster. Several galaxy groups are known to exist along the filament and this project will explore how star formation and morphology of galaxies are affected by the location of the galaxies and their distance from the centers of the two clusters. Starting from a list of candidate members based on spectroscopic and photometric literature redshifts, the student will perform accurate photometry with in-house software using at the same time archival images in the optical, infrared, and UV bands and will study the morphology of the galaxies using SDSS images. Star formation rates, stellar masses, morphological and spectral classifications will be derived for each member and related to the position along the filament and the density of the environment. This study on a relatively nearby system with multi-wavelength coverage from different public archives will shed new light on the processes involved in the evolution of galaxies infalling into clusters along filaments. Candidates with experience in either optical, infrared, or UV data and some software skills are welcomed.

In Search of the Coldest Atmospheres: Identifying Companions to the Latest WISE Brown Dwarfs Using HST

Advisor: Chris Gelino

Brown dwarfs are a class of objects with masses intermediate between stars and planets. Brown dwarfs with estimated effective temperatures below 500 K are just now starting to be discovered, filling in the gap between the coldest brown dwarfs and Jupiter-like planets (Teff=128K). The Wide-field Infrared Survey Explorer mission (WISE) is uncovering the closest, brightest examples of these objects, making them the best targets for further study. We are using the Keck II telescope in Hawaii and the Hubble Space Telescope (HST) to obtain high-resolution images of WISE brown dwarfs with spectral types T8 and later (Teff<700K) in order to search for companions down to effective temperatures of 300K. We have HST images in one or more filters of 36 brown dwarfs. The binaries discovered by this program will provide critical information for characterizing the properties of objects at the very bottom of the Main Sequence thus helping to bridge the modeling efforts between brown dwarfs and extrasolar planets. We are looking for a student to process and analyze the HST data using a combination of existing and to-be-written software. Experience with Python and/or IDL is preferred.

Measuring the mid-infrared extinction law in infrared-dark clouds

Advisor: Sean Carey

The project will use archival near-IR, Spitzer and Herschel photometry and Spitzer spectroscopy to measure the extinction curve from 2-70 microns for a set of infrared dark clouds. Infrared-dark clouds are the precursors to massive stars and stellar clusters and understanding the nature of the dust in these objects is vital to a better understanding of the process of massive star formation. In addition to measuring the extinction curve, a temperature independent measure of the column density will be made which can be used to better constrain temperature and emissivity variations at angular resolutions approaching 2 arcseconds. The evolution of the extinction curve and grain size as a function of increasing column density and by inference density will be measured.

Dust Chemistry and Mass Loss History of Massive Hot Stars

Advisors: Patrick Morris and Schuyler van Dyk

Stars with initial masses above 25 solar masses experience one or more episodes of significant mass loss from the stellar surfaces, in evolutionary transition from main sequence OB-type star to luminous blue variable (LBV) or Wolf-Rayet star before exploding as a supernova. These mass loss events may extend over several thousand years or in bursts, losing up to 2-3 solar masses in extreme cases like the famous LBV eta Carina, observable in circumstellar nebula with often spectacular displays of interactions between the present day stellar wind, previous mass loss events, and the ISM. The chemistry and physical properties of the dust formed and the mass loss history itself are tied to the evolution of the central star, and these are poorly known for more than only a couple of well known examples. Yet the near- and mid-IR colors of these objects can be used to identify visually-obsucred candidate Wolf-Rayet stars and LBVs from all sky surveys such as 2MASS and WISE, to reconcile the deficit of observed Wolf-Rayet stars versus evolution model predictions of numbers and lifetimes of this rare stellar class. We are looking for a student to refine the 2MaSS-based color selection scheme of Wolf-Rayet and progenitor LBV type stars, using the WISE all-sky survey incorporating the mid-IR colors which are influenced by line emission from the stellar wind and thermal properties of the circumstellar nebulae and interstellar redenning. The fundamental properties of known Wolf-Rayet stars will be described and quantified from imaging and spectroscopic observations taken with the Spitzer Space Telescope, the Infrared Space Observatory, and the Hershel Space Observaotry. The results will be strongly influential in the interpretations of massive stars and their energetics and chemical enrichment of the ISM in the Milky Way and other galaxies.

Understanding Luminous Infrared Galaxies with Herschel and Spitzer

Advisors: Lee Armus

Luminous Infrared Galaxies (LIRGs) generate their enormous power through intense starbursts and the fueling of Active Galactic Nuclei (AGN). With the Great Observatories All-sky LIRG Survey (GOALS), we are characterizing a sample of 202 low-redshift LIRGs across the electromagnetic spectrum (see A key part of GOALS is the study of the mid and far-infrared spectra of LIRGs as a function of power source, merger stage, and dust temperature. The infrared spectra are rich in emission and absorption features from dust, molecules, and neutral and ionized atomic gas. The successful candidate will work with the GOALS team at IPAC and the SSC to analyze Spitzer and Herschel spectra in order to constrain the energy sources and physical conditions in these rapidly evolving galaxies, and place them in context with high-redshift galaxies which will be studied with ALMA and JWST.

A Catalog of Periodicities in the Kepler Public Data Sets

Advisors: Bruce Berriman and Peter Plavchan

The community has only just begun to mine the extraordinarily rich science content of the public Kepler data sets. Our goal is to extend the scientific legacy of Kepler by using the high-performance compute services offered by Amazon Web Services (AWS) to create for public release a catalog of photometric variability periods present in the Kepler long-cadence (30 minutes) time-series data sets, currently numbering 2.3 million + for 190,000+ stars. The catalog will be generated by analysis of periodograms calculated for individual quarters of observations (~90 days time series), year-long light curves generated by stitching together four normalized individual long cadence quarter time-series, and a single time-series generated by stitching together the long cadence time-series for all quarters for each Kepler target.  As part of the pre-release validation effort, participating scientists and students will have exclusive access to the catalog for studies such as identification of differential stellar rotation from stellar activity cycles, and for sensitive searches for phase variations from non-transiting hot Jupiters that likely orbit ~1% of all Kepler targets undetected.