2021 Research Projects
Microlensing Parallax for Exoplanets Towards the Bulge
Advisor: S. Calchi Novati
The Spitzer team, in part based at IPAC, 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 (d > 1.5 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, Zhu et al 2017). Besides six exoplanets (Udalski et al 2015, Street et al 2016, Shvartzvald et al 2017, Ryu et al 2018, Calchi Novati et al 2018 and 2019), several additional interesting events (binary systems, high magnification events, single lens with finite source effects) have also been analyzed based on the first five years (2014-2018) of data, with the sixth season in 2019 expected to be the last one. In addition, relevant work is 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). In this framework there are several avenues to pursue, according to the applicant's interests and previous experience: optimizing the photometry of Spitzer data; characterization of microlensing events; evaluation of the detection efficiency.
Prior experience with microlensing is preferred but not required.
Shocked Gas in Compact Groups in the Local Universe.
Advisor: Phil Appleton
Understanding the evolution of star formation rates and gas content of galaxies in dense group environments may be important for explaining how massive galaxies are forged over cosmic time. We will study a small sample of Hickson Compact Groups, where galaxies are rapidly evolving through close collisional passes and mergers. We will concentrate on three galaxy groups for which XMM data has been taken (in collaboration with Ewan O’Sullivan at CfA) which shows extended X-ray emission which may be shock excited. We will compare these observations with extensive multi-wavelength data using optical IFUs (diffuse ionized gas), CARMA (cool molecular gas), as well as Herschel and Spitzer (warm neutral gas). This will allow us to explore the multi-phase nature of the gas in these systems, including the shocked IGM. The physical properties of these galaxies will be explored to try to understand how the shocks and turbulence may be influencing their evolution through tidal and collisional heating, gas stripping and eventual merger.
Measuring Accurate Distances to Stellar Streams
Advisor: Carl Grillmair
Our Milky Way Galaxy is enveloped by a network of stellar streams, the presumed remnants of old globular clusters and dwarf galaxies. These streams provide us with potentially powerful new tools for measuring the mass and shape of the Galaxy, as well as the makeup and distribution of dark matter. However, distance estimates to these streams remain one of the largest sources of uncertainty. We have recently obtained Spitzer IRAC time series images of RR Lyra stars found in a number of dynamically cold streams. One objective of this project would be to measure accurate mean infrared magnitudes for these stars and, by using the remarkably tight IR period-luminosity relation for RR Lyrae, to measure stream distances to better than 2%. The goal would be to publish these results towards by end of the fellowship. A second component of this project would be to analyze existing optical spectra of RR Lyrae taken at the Palomar 200 inch telescope. By measuring their radial velocities we can establish whether or not these RR Lyrae are physically associated with known streams. Stream members confirmed in this way will become part of a new target list for future infrared imaging and precise distance estimation.
Do young giant planets vary in brightness?: Assessing the cloud cover of the directly imaged HR 8799 planets.
Advisor: Tiffany Meshkat
It has long been assumed that planets maintain the same brightness over time. However, the presence of non-isotropic cloud structures in exoplanet atmospheres may cause variability in the planet brightness. Brown dwarfs have been shown to be variable. The nearest brown dwarf to Earth was found to be variable by 15% in certain wavelengths (Biller et al. 2013). This variability evolves on daily to weekly timescales (Gillon et al. 2013) and is likely due to changing cloud structures on these objects. Recent large scale surveys of brown dwarf variability with Spitzer reveal variability from a few percent to > 50% (Heinze et al. 2013). We may therefore expect to see variability in young exoplanets, which share similar effective temperatures and are similar ages. Indeed the young planet HR 8799 b (Konopacky et al. 2013) shares a nearly identical spectrum with the most variable brown dwarf known (2M2139, Radigan et al. 2012). The goal of this project is to reanalyze the vast amount of archival data on the HR 8799 bcde planets and assess the photometric variability over several timescales. We expect that a visiting graduate student would have experience using python or a similar programming language. With the guidance of Dr. Meshkat, the graduate student will process raw data on this star from several telescopes, detect the planets, and assess the brightness and error budget for that measurement. The data reduction methods and amount of photometric variation of the planets will be analyzed by the student in a publication.
Characterizing Planets via Near IR Precision Radial Velocity With an Innovative Spectrometer at The Palomar 5 m Telescope
Advisor: Chas Beichman
PARVI is a high spectral resolution, near-IR spectrometer presently being commissioned at Palomar 5 M telescope. A team of astronomers and engineers at JPL, Caltech and the American Museum of Natural History (AMNH) has developed a first-of-a-kind instrument --- PARVI, a diffraction limited system using the Palomar Adaptive Optics system to inject starlight into a single mode fiber fed to feed a compact, echelle spectrometer stabilized using a Laser Frequency Comb (LFC). PARVI has demonstrated R~90,000 spectroscopy in the J and H bands (1.1-1.8 μm) with an expected radial velocity precision (PRV) of 1-3 m/s. PARVI has already had successful commissioning runs in 2019 and was scheduled to begin science validation in 2020A before the Observatory was closed due to Covid-19. In the coming year the PARVI team will continue to optimize the sensitivity and stability of PARVI while demonstrating PARVI's capabilities in a number of key areas: 1) precision radial velocity (PRV) of transiting planets orbiting cool and/or young stars to determine their masses and orbits; 2) PRV measurements of mature planets in tight binaries; 3) Rossiter-McLauglin (RM) measurements to determine a planet's obliquity relative to the rotation of its host star; 4) direct detection of the spectra of a hot Jupiter via transit spectroscopy; and 5) exploration of the properties of stellar, sub-stellar and solar system objects at high spectral resolution. PARVI should be in routine operation by the 2021A semester.
The IPAC Graduate Visiting Student Program offers an opportunity for a graduate student to participate in the PARVI project in a number of ways, including optimizing instrument performance, defining and executing a specific observational program, or contributing to the Data Reduction and Analysis Pipelines in areas such as mitigation of telluric absorption or stellar activity.
Getting to Know Our Stellar Neighbors for Exoplanet Research
Advisor: Jessie Christiansen
Large astronomical surveys commonly rely on photometry to derive basic stellar properties, however, having a spectrum greatly expands the amount of information available for an object. With a spectrum it is common to use individual spectral lines to extract stellar properties, however, this method ignores the wealth of information a full spectrum provides, and it may mask degeneracies encoded in the spectral lines. There has been significant development recently to create tools to more precisely determine stellar properties either by forward modeling spectra from model grids (e.g., Starfish) or by comparing target spectra to a library of well-characterized stars (e.g., SpecMatch, The Cannon). Our team has a few thousand red-optical (~500-1000 nm) spectra of stars in the Kepler field, K2 fields, and the TESS northern continuous viewing zone for which we would like a visiting graduate student to precisely determine effective temperatures, surface gravities, and metallicities using the publicly available tools for stellar characterization. Combining these measurements with other data (e.g., Gaia parallaxes) will allow us to compute other stellar properties such as mass and radius, which will be used for exoplanet demographics studies. Familiarity with Python and computational Bayesian techniques is recommended.
Building Big Mosaics of the Sky: Studying the Low Surface Brightness Universe with TESS, and more!
Advisor: Bruce Berriman
The images delivered by the Transiting Exoplanet Sky Survey (TESS) offer a unique opportunity probe the low surface brightness Universe, primarily due to the exceptionally deep coverage at the ecliptic poles that is most likely limited only by zodiacal light. Thus TESS images will enable studies such as derivation of the halo profiles mass of nearby galaxies, tests of Lambda-CDM galaxy formation scenarios, derivation of stellar halo fractions for different mass and morphology galaxies and identification of local stellar streams that cross over sectors and other galaxy cannibalism leftovers. The student will join a small team of scientists and computer scientists analyzing the TESS images to address the science cases just described. The work will have a substantial technological component, and will involve using the Montage image mosaic engine to create analysis-ready mosaics of the sky as observed by TESS, and to understand the impact of background radiation on the science content of the images. The work will very likely provide the opportunity to perform computations on the Amazon Elastic Cloud. In addition the student will have the opportunity to create images delivered by TESS (and other missions) for consumption by the World Wide Telescope, a immersive E/PO environment used world wide.
Pathways to complex molecule formation through basic carbon chemistry in the Orion KL Star Forming Region
Advisors: Pat Morris (IPAC), John Pearson, Darek Lis (Caltech/JPL)
The formation of organic hydrocarbons in the ISM starts with the most basic ingredients of atmoic carbon, molecular hydrogen, and the simplest and most abundant C-bearing molecules such as CO. Yet the formation of those molecules, CO and highly reactive ionized CH in particular, is poorly understood, even in well-studied star forming regions (SFRs) such as in the Orion Molecular Cloud. This is because the chemical pathways depend strongly on the energetics, which can be dominated by UV radiation from young hot stars, or shocks from outflows, or both. And both are present in the Orion KL SFR. We have taken up the problem of how the CH+ molecule is formed and survives, requiring high energy input (endothermic processes), working well to match observed abundances under the conditions of a UV-dominated chemistry. However, no CH+ is observed where it was most expected, in shocked gas around the well-known outflow from the YSOs at the center of Orion KL. This may be a consequence of all carbon being tied up in CO formation, which can take different paths involving CO+, H2, OH, and HCO+. In other words, the formation of CH+ and CO has yet to be understood in this environment, with implications on basic carbon chemistry in other SFRs. We have far-IR/sub-millimeter observations from the Herschel Space Observatory and ground-based telescopes to solve this astrochemistry problem. The scholar will contribute by assembling and analyzing these data (becoming an expert in data reduction packages used at most ground-based sub-millimeter observatories), and contribute to or leading the publication of the results. A starting reference to this project is http://adsabs.harvard.edu/abs/2016ApJ...829...15M.
Exploring Star Formation with the PHANGS-HST survey
Advisor: Janice Lee
PHANGS-HST survey is a new program to build the first astronomical dataset charting the connections between young stars and gas, on the fundamental scales of star clusters and molecular clouds, throughout a diversity of galactic environments found in the local Universe. Though a Hubble Space Telescope (HST) Cycle 26 122 orbit Treasury Program, we are now obtaining NUV-U-B-V-I Wide-Field Camera 3 (WFC3) imaging for 38 galaxies, all with ALMA ~1” CO (2-1) maps from the PHANGS parent survey. PHANGS is the principal ALMA Large Program for nearby galaxies, and with ALMA and HST working in concert, PHANGS-HST will yield an unprecedented catalog of the observed and physical properties of ~100,000 star clusters, associations, and clouds. Our work will provide new constraints on star formation timescales, efficiencies, and the evolution of multi-scale structure as a function of galaxy-scale properties such as ISM phase balance, gas mass, star formation rate, surface densities, and galaxy morphology. These investigations are critical for informing a unified theory of star formation, gaining insight into galaxy scaling relationships such as the Kennicutt-Schmidt star formation law, and bridging the detailed study of star formation in Milky Way and select nearby galaxies, to the field of galaxy evolution. The joint HST-ALMA data products to be produced will be essential for maximizing the scientific return in a major area of study for JWST - dust embedded star formation - and will seed community science in star formation and beyond. A broad range of student projects are available, and ideas for new projects investigating star formation are welcome. https://sites.google.com/view/phangs/home
Probing the Atmospheres of the HotTESSt Jupiters
Advisor: Jessie Christiansen
The discovery of the first exoplanets completely changed our views of how planets form, specifically Jupiter-sized planets orbiting very close to their host star. Signs of the history and evolution of these planets are trapped in the chemical composition of the planetary atmospheres. For planets that form farther out and migrate in, we expect the amount of refractory material to be lower than the stellar abundance, but if the planet formed closer in, we might expect the refractory abundances to be higher than the stellar values. However, even in our own Solar System, it is not clear how the giant planets formed and acquired their abundances.
Our team is conducting a large survey program with the SOAR Telescope to obtain optical (~380-680 nm) transmission spectra of up to 30 hot Jupiters above 1700 K which were observed or discovered by TESS in order to constrain atmospheric oxygen and metal abundance through measurement of titanium oxide, vanadium oxide, and sodium features. We expect a visiting graduate student to work with our team on constraining atmospheric properties (e.g. abundances, Rayleigh scattering, clouds/hazes) of these hot Jupiters by comparing our transmission spectra to different publicly available atmospheric model grids. Familiarity with Python or other programming languages commonly used in astronomy is recommended.
A Spitzer-based Companion Search around the Nearest Stars
Advisors: J. Davy Kirkpatrick, Chris Gelino, Federico Marocco
One complication in accurately determining the single-object mass function at the lowest stellar masses is knowing the extent to which higher mass stars have lower mass companions of their own. Specifically, within a 20-pc radius around the Sun there are ~600 solivagant L, T and Y dwarfs known, but there are roughly 3,000 K and M dwarfs. If only a relatively small fraction of these K and M stars have faint companions, those companions could add appreciably to the sum of L, T, and Y dwarfs within the volume and therefore impact significantly on our understanding of the low-mass end of the mass function.
Data from the Infrared Array Camera (IRAC) in the Spitzer Heritage Archive (SHA) afford an exciting opportunity to look for widely separated faint companions around the Sun's closest neighbors, using both the 3.6-4.5 micron colors and, for fields with good epochal coverage, common proper motions. This will be the first opportunity anyone has had to search through the *entirety* of the SHA for companions, as all Spitzer data will be just beyond their proprietary periods by the time of this Visiting Graduate Fellowship appointment. Fields to be searched will include not only those from programs specifically targeting the host star, but also fields observed serendipitously around the 0.1-pc tidal radius around any of those potential hosts. Note that Spitzer data complement Gaia data because these coldest companions are not observable at the shorter wavelengths of Gaia.
All three mentors have extensive experience with Spitzer data. Our plan is to have the student spend the Fellowship examining data in the SHA for previously hidden companions, while placing constraints on the percentage of the 0.1-pc physical radius covered by the data and the depths to which low-mass companions could be found. The student will start with those stars closest to the Sun and proceed outward in distance until the two-thirds point in the Fellowship is reached (with a stretch goal of completing the work for the entire 20-pc sample). In the final third of the Fellowship, the student will begin writing, as lead author, a publishable paper summarizing the results over that completed search volume.
Characterizing High-Redshift Galaxies with ALPINE
Advisor: Andreas Faisst
The ALPINE project is a 70h large ALMA program aimed at characterizing the far infrared (FIR) and [CII] (158um) properties of 4<z<6 galaxies. We seek students to work on combining the extensive existing multi-wavelength imaging and spectroscopy with the ALMA data to conduct a range of studies. These could include studies of the main-sequence of galaxy evolution, evolution of the far-infrared luminosity function, the dust properties of high-redshift galaxies and comparing [CII] dynamics with estimates of galaxy physical parameters.
Identifying Stars with Machine Learning for the Next Generation of Surveys
Advisors: Andreas Faisst & Roberta Paladini, Sergio Fajardo-Acosta, and Ranga Ram Chary
Surveys with the next generation of telescopes (such as LSST, WFIRST, or Euclid) rely on a statistically accurate identification of stars and compact sources. These are used as astrometric references and for identifying candidate quasars. On one hand, stars are necessary for proper astrometric alignment, which is crucial for the joint cataloging of datasets from these various missions across a large range of wavelengths, seeing conditions, and time intervals. Furthermore, proper alignment is essential to search for asteroids and other moving objects in the sky. On the other hand, the identification of faint stars and the measurement of their proper motion over time from different datasets itself builds a strong science case for the study of stellar streams in our galaxy and/or kinematics of our Galaxy and nearby galaxies.
We seek a student as part of our Joint Survey Processing (JSP) group to implement and test a machine learning framework to identify isolated and unsaturated compact objects in future datasets. Specifically, the successful candidate will train this framework and perform various tests using realistic simulated images from LSST, Euclid, and WFIRST (which will be created as the first part of the project). The trained model will be tested on real data on the COSMOS field, which is the closest to future combined ground and space-based datasets.
CLU: A Galaxy Survey as Part of the Search for Gravitational Waves
Advisor: David Cook
The Census of the Local Universe (CLU) is a survey that aims to find new galaxies in the nearby Universe (out to a distance of 200~Mpc; z~0.05). We utilize four wavelength-adjacent narrow-band filters to search for Halpha emission-line sources across 3pi (~26,470 deg^2) of the sky; roughly the footprint of Pan-STARRS. A preliminary analysis of the data has yielded thousands of nearby galaxy candidates that are being used to augment lists of known galaxy inside the LIGO/Virgo gravitational waves (GW) sensitivity distance limit (See paper: https://ui.adsabs.harvard.edu/abs/2019ApJ...880....7C/abstract). However, we expect find many 10s of thousands more with refinements to the data processing and analysis. These additional candidates will increase the completeness of galaxies in the local volume and further narrow down the search for counterparts to GW events.
The prospective student's main focus in the project would be to devise and implement an "uber" photometric calibration of the 4 narrow-band filters. However, there are many opportunities to be involved in several aspects of the project including: galaxy finding algorithms, applying photo-z methods (both SED fitting and machine learning) to test distance estimates, vetting galaxy candidates, interacting with a large GW follow-up group here at Caltech/IPAC, analysis of extreme local star-forming galaxies (blue compact dwarfs and green peas), and getting first-hand observing experience at Palomar Observatory. We are looking for a student with experience in data reduction and calibration; python and PSQL/SQL data languages are a plus.
Challenging Planet Formation Theories with the Lowest Metallicity TESS Targets
Advisor: Jessie Christiansen
Previous studies of exoplanet demographics have shown that planet occurrence rates depend on the bulk metallicity of the host star. This is a natural outcome of the core accretion model of planet formation. This model also predicts that below a certain protoplanetary disk metallicity, there is too low a surface density of solid material to form planets. Due to the target selection process of previous large surveys, the lower metallicity bound probed by the results in the literature ([Fe/H] ~ -0.5) is still higher than that predicted to be too low to support planet formation ([Fe/H] < -1). Our team received a Director’s Discretionary Time allocation on the NASA TESS mission to observe several thousand of the brightest, lowest metallicity ([Fe/H] < -1) stars in the sky at high cadence, in order to provide a fundamental observational test of these theoretical predictions. A visiting graduate student fellow would be expected to examine this sample for planet candidates, using code that the team has already developed and tested on TESS data. Any confirmed planets from the sample would already challenge existing models, and a null result would produce strong upper limits. The fellow would gain experience in planet detection and characterization, as well as occurrence rate modeling using Bayesian methods.
WISEsize: Probing Gas Consumption and Stripping in Local Spirals with WISE
Advisor: Vandana Desai
While it has been known for decades that galaxy clusters and groups harbor a low fraction of star-forming galaxies, a lively debate continues over how star formation is quenched, and at what environmental densities. The primary science objective of this project is to understand how galaxies are altered as they move through the cosmic web and enter the densest regions. We will use the relative extent of the star-forming and stellar disks to probe environmental quenching because environmentally-driven gas depletion is expected to preferentially remove gas from the outskirts of galaxies. This proposal outlines our plans to measure the spatial extent of the star formation relative to the stellar disk for 14,000 star-forming galaxies in the nearby universe (0.005 < z < 0.030). The all-sky coverage of WISE lets us probe the full range of galactic environments. This work builds on initial results carried out with Spitzer data by Finn, Desai, Rudnick, et al. (2018).
Probing Dark Energy with Galaxy Clustering
Advisors: Yun Wang, Zhongxu Zhai
Galaxy clustering is one of the most powerful probes of dark energy, the unknown nature of the observed cosmic acceleration. NASA's next flagship in astrophysics, Roman Space Telescope, will carry out a large area galaxy redshift survey to provide constraints on dark energy using galaxy clustering. We are developing realistic galaxy mock catalogues for the Roman Space Telescope, derived from cosmological N-body simulations and a semi-analytical galaxy formation model GALACTICUS. We are interested in a graduate student working with us to use these mock catalogues to study how well the Roman Space Telescope data can constrain dark energy and cosmological parameters using galaxy clustering.
Estimating the Galactic Metallicity with Herschel Spectroscopy
Advisor: Roberta Paladini
The metallicity of gas and stars in galaxies is one of the most important properties to distinguish among evolutionary scenarios, as metals are the results of the cumulative star-formation activity of the galaxy and of its gas inflow/outflow history. The gas metallicity is in most cases much easier to measure than stellar metallicity, and the most favorable environment where to perform this kind of measurement is the interior of HII regions, i.e. ionized pockets of material surrounding massive OB stars, which are largely understood and tested.
The tool commonly used to estimate gas metallicity is atomic fine-structure emission lines radiated by various ions on various excitation levels. In particular, the use of mid-infrared to sub-millimeter emission lines allows one to overcome the extinction problem that plagues optical measurements.
In this project, we propose to use Herschel PACS and SPIRE spectroscopic data for a sample of Galactic HII regions in order to determine the Galactic gas metallicity as well as the HII regions ionization state and its variation as a function of Galactocentric distance. This study will provide the calibration at redshift zero for the metallicity - reshift relation and will inform galactic evolutionary models in view of future space mission such as OST and SPICA.
