2020 Research Projects
UKIRT Microlensing Survey: A Pathfinder for WFIRST
Advisors: Y. Shvartzvald and S. Calchi Novati
The microlensing team based in Pasadena (IPAC and JPL) is currently leading the first near-infrared (NIR) microlensing survey towards the Galactic Bulge, using the 3.8 UKIRT telescope on Mauna Kea, as a precursor of the WFIRST microlensing survey, which will complete the statistical census of planetary systems in the Galaxy (Spergel et al. 2015, Penny et al. 2019). Two UKIRT surveys have already been conducted in 2015 and 2016, in conjunction and support with the Spitzer microlensing campaign and the K2C9 program (Henderson et al, 2016), with the main goal to combine ground and space-based data to characterize the lens systems through the measure of the microlensing parallax. In particular, together with Spitzer, UKIRT data have been key for the analysis of a massive remnant, possibly a black hole, in a well-separated binary in the Galactic Bulge (Shvartzvald et al 2015). UKIRT data are routinely being used in conjunction with other ground base microlensing data to characterize exoplanets (Koshimoto et al. 2017, Han et al. 2017, Ryu et al. 2018, Hwang et al. 2018) and other binary lens events (Han et al 2018). In addition, out of 2017 UKIRT data a planet was detected at 0.35 deg from the Galactic center, pushing for the first time planetary microlensing in such high-extinction regime (Shvartzvald et al, 2018), in a region not accessible to optical-based survey.
While continuing as support for optical ground-base surveys and the Spitzer program, the main goal of the currently ongoing UKIRT survey, 2017-2019, is to map the microlensing event rate across the highly extinguished region across the Galactic center, which is key for field selection and optimization of the forecoming WFIRST survey. Indeed, besides the detection and characterization of exoplanets, microlensing is a powerful tool for the understanding of the overall underlying Galactic structure, and the analysis in the NIR (in H and K bands) allows to probe, for the first time, the region right across the Galactic center.
A pilot analysis reporting 5 microlensing events that were not detected by optical surveys due of the high extinction has already been carried out (Shvartzvald et al, 2017). In this framework, there are several avenues to pursue, according to the applicant's interests and previous experience: the development of the photometry pipeline; the analysis of specific interesting events; the development of a selection pipeline for microlensing signal with machine-learning tools; a map for the extinction in the inner Galactic region. Prior experience with microlensing is preferred but not required.
Characterizing Galaxies with the ALPINE Project
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.
Understanding the Role of Stellar Multiplicity in the Formation and Evolution of Planetary Systems
Advisor: David Ciardi
The Kepler and K2 Mission have revolutionized our understanding of the size distribution and frequency of planets around other stars. Characterization of the planet host stars and the assessment of the photometric blending of the host stars with bound and background stars are crucial to the accurate determination of the stellar and planetary radii. Without an assessment of the photometric blending of the host stars, an accurate determination of the planet sizes is impossible. Over the past 10 years, we have undertaken a systematic survey of the Kepler and K2 planetary candidates with high spatial resolution adaptive optics and speckle imaging to detect binary companions. And with TESS starting science operations this summer and the large number of nearby targets around which TESS will find planets, we will be able to address the questions of stellar multiplicity in planet hosting stars in ever increasing detail.
We are looking for a student with experience in high spatial resolution imaging to analyze the speckle and AO data for TESS planet hosting stars (along with a control sample of stars) to determine the stellar multiplicity rates of the TESS stars, to determine the true sizes of the planetary candidates, and to assess the relationship between stellar multiplicity and planetary occurrence.
Microlensing Parallax for Exoplanets Towards the Bulge
Advisor: S. Calchi Novati and Sean Carey
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, and 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.
Characterizing the Galaxy Population with Machine Learning
Advisor: Peter Capak
We have developed a set of new techniques that use machine learning to model galaxy evolution surveys in a statistical manner and map the statistical model to a range of galaxy property measurements. This has the advantage of being able to easily model and understand systematics in the data and map that to systematics in the final measurements of physical parameters.
We are seeking students to interested in working with machine learning techniques to develop and extend our framework.
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.
Galaxy Evolution with the Spitzer Legacy and Hawaii-2-0 Survey
Advisor: Peter Capak
The Spitzer Legacy and Hawaii-2-0 survey is an ambitious program to cover 20 square degrees around the Chandra Deep Field South and the North Ecliptic Pole with Spitzer and Hyper-Suprime-Cam. The survey consists of 5500h of Spitzer, 30 nights of Hyper-Suprime-Cam, and 10 nights of Keck data and started in late 2017.
The overall goal is to find and characterize rare and high-mass galaxies at z>4 and link those objects to their dark matter halo’s. We are seeking students to work with the first year of Hyper-Suprime-Cam data on these fields with the goal of identifying rare and interesting high-redshift targets for follow-up with Keck and JWST.
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.
The BUFFALO Project
Advisor: Peter Capak
The BUFFALO project is a 101 orbit HST program which aims to better characterize the z>7 universe by extending the HST coverage around the Frontier Fields lensing clusters. This increased area should more than double the number of bright galaxies known at these redshifts.
We are seeking students to work on finding and characterizing high-redshift galaxies in the HST data which will start arriving in the summer of 2018.
Probing the Atmospheres of the HotTESSt Jupiters
Advisor: Kevin Hardegree-Ullman and 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 farther 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.
In its first two years of operation, the Transiting Exoplanet Survey Satellite (TESS) is expected to detect over 100 hot Jupiters. We have begun a large survey program to obtain optical (380-650 nm) transmission spectra of ~30 hot Jupiters above 2,000 K discovered primarily 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 would work 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.
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.
Cosmology With Euclid, WFIRST, and SPHEREx
Advisor: Peter Capak
We are seeking students to work on developing techniques for precision weak lensing cosmology, baryon acoustic oscillations, or inflation cosmology. The student would work with the Euclid, WFIRST, and SPHEREx groups at IPAC to develop techniques and simulations to carry out these missions. Current areas of focus include: calibration of photometric redshifts, construction of weak lensing tomographic bins, improved methods for joint photo-z and weak lensing analysis, joint photometric and spectroscopic analysis of the grism data, and modeling of the galaxy population.
The Euclid mission will conduct a 15,000 square degree imaging and grism spectroscopic survey aimed at measuring the nature of dark matter and dark energy starting in 2021. The WFIRST mission is under development and will use similar, but more sensitive probes of dark energy starting in the mid to late 2020s. SPHEREx is a recently selected mid-scale satellite that will spectrocopically survey the entire sky at 0.75-5um with a spectral resolution of R~34-150 and a spatial resolution of 6.2".
Pathways to Complex Molecule Formation Through Basic Carbon Chemistry in the Orion KL Star Forming Region
Advisor: Pat Morris, John Pearson and Darek Lis
The formation of organic hydrocarbons in the ISM starts with the most basic ingredients of atomic 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 student 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.
Understanding Star Formation and Black Hole Growth in Luminous Infrared Galaxies
Advisor: Lee Armus, Joe Mazzarella 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 over 200 low-redshift LIRGs across the electromagnetic spectrum.
A key part of GOALS is the study of how stars form and black holes grow under these extreme conditions, by observing the atomic and molecular gas and star clusters at high resolution. To this end, we have been obtaining imaging and spectroscopic observations of LIRGs with HST, ALMA. Palomar and Keck/AO in the UV through the sub-mm.
The successful candidate will work directly with the GOALS team to reduce, analyze and publish recent observations of the star-forming clusters, molecular gas content, and galactic outflows in LIRGs, placing them in context with normal galaxies in the local Universe, and high-redshift dusty galaxies at z > 2. The student will also work with the team to prepare for upcoming observations of GOALS sources with JWST, as part of an awarded Director’s Discretionary Early Release Science (ERS) program, and proposals for the first GO call.
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. Through 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.
Getting to Know Our Stellar Neighbors for Exoplanet Research
Advisor: Kevin Hardegree-Ullman and 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 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). We have in hand 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 are extremely valuable for exoplanet studies. Familiarity with Python and computational Bayesian techniques is recommended.
