2017 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.

Application Instructions

The call for 2017 applications is open, please submit your applications. Applications are due by August 30 2016.

  1. A brief letter of introduction indicating your interest in a particular research area connected with IPAC research. The letter should include the following information:
    • A brief description of your current status as a graduate student, including relevant course work completed.
    • A brief description of how your current research interests might match one of the IPAC research projects described below. Please rank the top 3 projects that you might like to participate in. 
    • Please list any research experience you may already have in astronomy. In addition, please tell us of any experience you may have with astronomical and image processing software packages (e. g. IRAF, IDL, HIPE, AIPS etc).
    • The approximate start-date of your visit (nominally early Jan 2016).
  2. A one-page CV.

In addition, we ask that a current professor or academic advisor familiar with the applicant’s work upload a letter of reference (PDF) using this page. This letter should also indicate that the applicant is available to visit IPAC during the proposed period, and address how well the visit would mesh with the applicant’s graduate education.

Description of Research Projects

Microlensing Parallax for Exoplanets Towards the Bulge

Advisors: Sebastiano Calchi Novati and Sean Carey

The Spitzer team (PI: A. Gould) is leading a microlensing observational campaign towards the Galactic Bulge following up microlensing events alerted by ground-based surveys. The key feature of this project is the possibility to measure the microlensing parallax thanks to the simultaneous observation of the same microlensing event from two distant (of order AU) observers (from Earth and from Spitzer). The main scientific driver of the project is to build the Galactic distribution of exoplanets (Calchi Novati et al, 2015a). Besides two exoplanets (Udalski et al 2015, Street et al 2016), several additional interesting events (binary systems, high magnification events, single lens with finite source effects) have also been analysed based on the first two years (2014 and 2015) of data (Yee et al 2015a, Zhu et al 2015a, Shvartzvald et al 2016, Bozza et al, 2016, Poleski et al 2016, Zhu et al 2016). In addition, relevant works are being done for the analysis of the data (Calchi Novati et al 2015b) and to assess the statistical meaning of the observations (Yee et al 2015b, Zhu et al 2015b). Following the third season, in 2016, there is a plan to continue observations in 2017-2018. In this framework there are several avenues to pursue, according to the applicant's interests and previous experience: planning for the 2017-2018 campaign; photometry of Spitzer data; characterization of microlensing events; evaluation of the detection efficiency. Previous experience with microlensing analysis is preferred.

Observing Galactic Superwinds with the Cosmic Web Imager

Advisor: Lee Armus

Galactic-scale winds, or 'Superwinds', driven by the collective effect of massive stars and supernovae, have been invoked as a source for the heating and metal-enrichment of both the intra-cluster and inter-galactic medium, as a critical factor in the evolution of galaxies, and as the source of the mass-metallicity relation for galaxies. It has also been suggested that superwinds are a natural and necessary transition phase in the evolution of powerful starbursts to QSOs, and that they may clear channels allowing ionizing photons to escape into the CGM. We are continuing a project to study the optical emission-line nebulae and outflowing superwinds in a sample of nearby starburst and infrared luminous galaxies using the Cosmic Web Imager - a new wide-field, image slicing, optical integral field spectrograph on the Palomar Hale 200-inch Telescope. With an acrminute field of view and a resolution of R~5000, CWI enables detailed studies of an important piece of the local cosmic web. We are combining these CWI data with Keck/OSIRIS near-infrared LGS/AO observations and HST narrow-band imaging to trace the ionized atomic and warm molecular gas, as well as the escaping ionizing radiation, on scales ranging from 0.05 - 50 kpc. The student will participate in the observing, data reduction and analysis, and publication of the CWI and ancillary data.

Understanding Luminous Infrared Galaxies with Infrared Spectroscopy and Spectral Energy Distributions

Advisors: Joe Mazzarella, Lee Armus, and the GOALS Team

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 http://goals.ipac.caltech.edu). A key part of GOALS is the study of the mid and far-infrared spectra and spectral energy distributions (SEDs) of LIRGs as a function of power source, merger stage, and gas content. The infrared spectra are rich in emission and absorption features from dust, molecules, and neutral and ionized atomic gas, as well as powerful continuum emission from dust at a wide variety of temperatures. The successful candidate will work with the GOALS team at IPAC to analyze Spitzer, Herschel, HST, ALMA, JVLA, NuSTAR and other ground and space-based data in order to constrain the energy sources and physical conditions in these rapidly evolving galaxies. Multiwavelength data in the NASA/IPAC Extragalactic Database (NED) will also be used to analyze the widest frequency range possible (X-rays through radio) for each system. The successful candidate will work directly with the GOALS team to help understand the physical conditions driving the powerful starbursts and AGN in LIRGs, placing them in context with normal galaxies in the local Universe, and high-redshift dusty galaxies being studied now with ALMA. The student will also work with the team to plan for future observations of nearby and high-redshift LIRGs with JWST.

Herschel Legacy Survey of Hydrides in Nearby Galaxies

Advisor: Pat Morris

We are conducting a comprehensive survey of hydrogen fluoride (HF) and water molecular lines in nearby galaxies from the archival Herschel/HIFI, SPIRE and PACS spectra. Absorption of HF along sight-lines to bright continuum sources is revealed by Hershel observations to be ubiquitous in the Milky Way; models predict that this simple molecule is the dominant reservoir of interstellar fluorine under a wide range of conditions, providing a unique probe of the kinematics of -- and depletion within -- clouds in the ISM. Our studies further revealed that the ground state transition of HF and water in the Galactic disk probe the same gas-phase volume, with HF abundances comparable to those of water.

We will consolidate all the ground state transition of HF and H2O - as well as multi excitation transitions of H2O -- towards nearby galaxies obtained with Herschel. The objective of this survey is to probe the chemistry of fluorine and oxygen-bearing molecules and to determine to what extent both species can be used as diagnostic of the physical process at play in the ISM of the host galaxy. With our studies we will determine the main excitation mechanism of HF - whether is collision with electrons, IR or chemical pumping - in nearby galaxies and provide a steady template on the chemistry and physics conditions of the ISM in the local universe that can be used to understand the early universe where observations of hydride molecules are more scarce. We are looking for a student with knowledge or interest in astrochemistry and Herschel/HIFI, SPIRE and PACS spectroscopic data analysis. With Drs. Pat Morris (IPAC) and Raquel R. Monje (JPL), the student will participate in processing, analysis, and interpretation of high quality products from the Herschel Legacy Archive, and work towards a publication on the initial results.

Understanding Extreme LINERs in the Local Universe: Shocked Galaxies OR Heavily Obscured AGN?

Advisor: Philip Appleton

We have defined a sample of galaxies with unusual optical emission line properties based on the SDSS spectral line survey. Out of 68,000 galaxies, we have discovered 50 galaxies with extreme emission line properties with median redshifts of 0.1. The galaxies are quite large and contain gas with very low excitation as measured by the ratio of [OIII]/H_beta, but have very large [OI]/H_alpha ratios (Extreme LINER). The project will involve building an understanding of the UV/opt/IR spectral energy distributions of these galaxies, and how they fit into an understanding of galaxy evolution. We are conducting a major Palomar near-IR survey of a subset of the galaxies to look for evidence that many of these galaxies are dominated by large-scale shocks. The project has implications for future large scale emission line surveys of galaxies at high redshift, such a WFIRST.

Selecting the best targets for JWST using Spitzer and K2

Advisor: Jessie Christiansen

The NASA Kepler mission has been performing the K2 survey for two years now – an ecliptic plane photometric survey obtaining very high precision light curves on tens of thousands of stars. The CHAI (California-Hawaii-Arizona-Indiana) collaboration is focused on discovering, confirming and characterising extrasolar planets in the K2 data. One critical part of our followup and characterisation of candidate planets is through Spitzer observations. We were awarded a Cycle 11 GO program (PI Werner; 455 hours) to observe our candidates, initially focussing on observing candidates orbiting M dwarf stars and later expanding the survey to include FGK dwarf stars. Our goal is to identify the most promising candidates for JWST follow-up, via confirmation of planethood, refinement of system parameters (including ephemerides), and identification of additional aspects of interest like transit timing variations or detectable secondary eclipses. Several of the observations have been published (Beichman et al. 2016; Benneke et al. 2016) but we have additional data that need reduction. Furthermore, we have proposed for a large Cycle 12 program to continue working on K2 candidates and, if the timing is favourable, TESS candidates for the next two years. We expect that a visiting graduate student would work with the Spitzer data, improving and refining the data reduction techniques, modelling the transit parameters, and publishing results.

Spectroscopic Follow-Up of AllWISE/AllWISE2 High Motion Surveys

Advisor: Sergio Fajardo-Acosta

The AllWISE Data Release provides apparent motion measurements for all sources detected in coadded images made from the WISE (All-Sky + 3-Band Cryo) and NEOWISE (Post-Cryo) missions. A first catalog of motion objects from this Data Release was published in Kirkpatrick et al. (2014) and included 3,525 discoveries over the entire sky. At the same time, Luhman (2014) discovered 762 objects from standard WISE processing. These data hinted at the potential for even more discoveries, after modification of AllWISE selection criteria for bona fide high motion sources. We completed a new all-sky search, dubbed "AllWISE2," using improved selection criteria. Kirkpatrick et al. (2016) published the AllWISE2results, in the form of a catalog with an additional 28,000 motion objects, as well as 17,000 known motion objects from the original AllWISE survey. Therefore, the AllWISE and AllWISE2 surveys have yielded 48,000 motion objects.

From our list of AllWISE and AllWISE2 discoveries, we have identified candidates for spectroscopic follow-up and characterization, first using color-color, color-mag, and color-motion space. These candidates point in some cases to unusual systems, such as cold white dwarfs of spectral varieties not previously seen. Other systems may be binaries of brown dwarfs of peculiar abundances. We may also be seeing single nearby stars with atmospheric phenomena of an entirely new nature.

We are carrying out optical and near infrared spectroscopy of the above candidates, using the Double Spectrograph at the Hale Telescope at Palomar Observatory, and the SpeX near-infrared spectrograph at the NASA Infrared telescope Facility, among others. We expect the graduate student to assist with these observations, and with interpretation and publication of results.

The graduate student may also choose a topic of study of his/her own for high motion objects from the above surveys.

Requirements are a basic knowledge of brown dwarf theory, and familiarity with optical and near-infrared spectroscopy. Knowledge of white dwarf theory is a plus. Familiarity with programming languages such as IDL and IRAF, the IRSA catalog search tools, and imaging datasets such as WISE/NEOWISE and 2MASS is recommended.

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