2019 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 3.8m 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). The main purpose of the ongoing survey 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. Shvartzvald et al (2017) presented the UKIRT pilot analysis to that purpose, reporting in particular the detection of 5 microlensing events that were not detected by optical surveys due of the high extinction. At the same time, UKIRT microlensing data are being used for the discovery and the characterization of exoplanets, by themselves as well as in conjunction with the current ground-based optical surveys and the ongoing space-based Spitzer microlensing campaign. In particular, Shvartzvald et al (2018) presented the first NIR microlensing planet lying only 0.35 degree from the Galactic center; Shvartzvald et al 2015 discussed a massive remnant, possibly a black hole, in a well-separated binary in the Galactic Bulge; finally, UKIRT data were used in the analysis of four additional planets (Koshimoto et al, 2017; Han et al, 2017; Hwang et al, 2018 and Ryu et al, 2018).
Within 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.
Short-timescale variability of blazars
Advisor: Ranga-Ram Chary
Blazars, which are powered by supermassive black holes, are responsible for the most energetic and violent GeV/TeV gamma-ray flares in the Universe. The canonical thinking is that these flares arise from Compton up-scattering of low-energy photons in the relativistic jet which is aligned along the line of sight. Short timescale variability analysis between the radio/millimeter intensity and the gamma-rays can help constrain the origin of the gamma-ray emission. The Planck mission data archived at IPAC provides a unique capability to measure the short (~day to week) timescale variability of gamma-ray blazars over nine frequencies. The student will download Planck data, generate light curves and spectral indices of blazars at various frequencies, compare with the measured intensity of Fermi/LAT gamma-ray emission and try to constrain the physical processes that occur prior to a gamma-ray flare. The duty cycle of flaring will also help obtain a better constraint on the contribution of blazars to the high energy extragalactic gamma-ray background
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: Sean Carey
The Spitzer team (led by A. Gould, J. Yee and S. Carey) is carrying out 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). In addition to five exoplanets (Udalski et al, 2015; Street et al, 2016; Shvartzvald et al, 2017; Ryu et al, 2018; Calchi Novati et al, 2018), several interesting events (binary systems, high magnification events, single lens with finite source effects) have also been analyzed based on the first four years of data (2014, 2015, 2016 and 2017), resulting in more than 20 additional refereed publications (submitted or published). In parallel, Calchi Novati et al (2015b) developed the specific algorithm for the photometry of time series of Spitzer data in the crowded Galactic region; Yee et al (2015) and Zhu et al (2015) set the basis to assess the statistical meaning of the observations. The Spitzer microlensing campaign is currently ongoing during the two years of the ``Spitzer Beyond'' phase (2017-2018).
In this framework there are several avenues to pursue, according to the applicant's interests and previous experience: planning for the observational campaign; optimizing the photometry of Spitzer data; characterization of microlensing events; evaluation of the detection efficiency.
Archival IRAC Light Curves: Comparative Exoplanet Atmospheres
Advisors: Jessica Krick and Jessie Christiansen
One of the great legacies of the NASA Spitzer mission Infrared Array Camera (IRAC) will be its contribution to the field of extrasolar planets. The publicly available IRAC data archive is incredibly rich, including roughly 1500 exoplanet observations in either transit, eclipse, or over full phase curves. However, the majority of these observations have not been published, and those that are already in the literature have typically been studied as individual sources using data reduction techniques tailored to each observation. We propose a project to do comparative exoplanet atmospheres using a uniform reduction of the entire public IRAC exoplanet archive. The database has been designed, built, and populated with photometry using a novel, machine-learning based, noise removal technique. We are now looking for an interested grad student to work on either an interface to the database or assemble a sub-sample of all observed exoplanet with eclipse observations in both channels from the database to examine the relative strengths of the 3.6-micron and 4.5-micron eclipse depths as a function of planet mass to study planet formation theories linking planet mass and atmospheric metal content.
Do young giant planets vary in brightness?: Assessing the photometric variation 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 on 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.
Thick disks as witness of the early assembly history of galaxies
Advisor: Marja K. Seidel
The origin and formation of thick disks is still unclear. The discovery of the Milky Way’s thick disk in 1983 (Gilmore & Reid 1983) triggered a growing body of evidence that it is a structurally, chemically, and kinematically distinct component of the Galaxy. It is considered to be a relic of the early Galactic disk. As such, the thick disk provides an excellent probe of models of disk galaxy formation. But how do thick disks form? Several mechanisms have been proposed, including: (a) energetic early star-forming events, (b) accretion debris, (c) heating of the thin disk via disruption of its early massive clusters, and (d) early-formed thin disks, heated by accretion events such as the one, which is believed to have brought omega Centauri into the Galaxy. Detailed comparisons of thin and thick disk properties are required to test these formation models. In particular, the combination of kinematics, relative ages and chemical enrichment patterns of the thin and thick disks can discriminate between these formation models. We plan a detailed study of the kinematic and stellar population properties of the thin and thick disk using integrated spectra acquired with the LDSS3 spectrograph on the 6.5m Magellan Clay telescope along various heights of the edge-on disk. Observations were successfully completed in December 2018 and the student will be in charge of all the aspects of this project, making it his/her own project, including reducing the spectra, obtaining the kinematic and stellar population measurements along the various heights of the disk, and most importantly writing up the final results in a first-author paper presenting intriguing results on this external thick disk system, allowing us to better understand the early galaxy assembly history.
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.
Exploring Frontier fields in 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.
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 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.
Calculating Occurrence Rates with K2
Advisor: Jessie Christiansen
Measuring the occurrence rate of extrasolar planets is one of the most fundamental constraints on our understanding of planets throughout the Galaxy. By studying planet populations across a wide parameter space in stellar age, type, metallicity, and multiplicity, we can inform planet formation, migration and evolution theories. In the post-Kepler era, our collaboration has been compiling catalogues of planet candidates from the K2 mission (see, e.g. Crossfield et al. 2016), and has expended considerable effort in characterizing the resulting planetary systems through a large follow-up program. With the full K2 data-set expected to be in hand by the start of this proposed project, we are interested in investigating the underlying planet population. In particular, since K2 has observed nearly an order of magnitude more M-dwarfs than Kepler, we aim to constrain occurrence rates both more precisely and with more granularity across the broad M-dwarf parameter range than previously. We expect that a visiting graduate student would work on and publish an aspect of the occurrence rate calculations that they were interested/experienced in, such as: examining biases between planet host and non-planet host stars; coordinating and performing follow-up observations of candidates with high-resolution imaging or reconnaissance spectra; or developing and implementing algorithms to automate planet candidate selection for generating a uniform, repeatable, quantifiable final planet c A
Using High Spectral Resolution Data to Characterize Exoplanets
Advisors: Chas Beichman / Marie Ygouf
Post-processing techniques developed for high-contrast imaging can be applied to data from high-spectral resolution Integral Field Spectrometers (IFSs) to characterize the atmosphere of the brightest exoplanets, e.g. HR8799b spectra obtained using Keck-OSIRIS [Bowler et al. 2010]. The main limitation of IFS observations toward exoplanets orbiting bright stars is the presence of speckles, which create systematic errors that are difficult to calibrate and remove. A strategy of speckle cancellation with high potential exploits the wavelength diversity offered by an IFS and is called Spectral Differential Imaging (SDI). Some empirical methods, based on a speckle intensity calibration in the focal plane, have been developed to subtract the speckle field from the image [Sparks et al. 2002, Soummer et al. 2012, Lafrenière et al. 2017]. However, in these methods crucial prior information inferred from the instrument is not used as an input for post-processing. The Medusae (Multispectral Exoplanet Detection Using Simultaneous Aberration Estimation) algorithm [Ygouf et al. 2013] is based on an analytical model of multispectral coronagraphic imaging and an inversion algorithm. The technique estimates jointly the instrumental aberrations and the object of interest, i.e. the exoplanets, in order to separate properly these two contributions. The inversion algorithm is based on a maximum-likelihood estimator, which measures the discrepancy between the multispectral data from an IFS and the imaging model. It is then possible to retrieve, from multispectral images, an estimation of the aberration map and of the position and flux of the planets at each wavelength and thus their spectra.
We expect that a visiting graduate student would work to improve and adapt the Medusae algorithm to non-coronagraphic IFS data. For this purpose, the student will test and validate the technique on both simulated data and on archival data of the Keck-OSIRIS instrument. This work is an essential step toward the application of this technique to other instruments such as the WFIRST coronagraph or future high-dispersion coronagraphs [Mawet et al. 2017].
Characterizing Galaxies with the ALPINE project
Advisor: Peter Capak
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.
Using machine learning to model the galaxy population in cosmology surveys
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.
Star Formation Quenching in Galaxy Clusters using Spitzer
Advisor: Vandana Desai
A crucial component to the study of galaxy evolution is a good understanding of the mechanisms by which star formation is enhanced or suppressed. Previous observations show that galaxies residing in over dense regions of the universe are more likely to be passive than their relatively isolated field counterparts, indicating environmental influence on star formation. In addition to this evidence of external means of suppression, both cluster and field populations show declining star formation activity over time at z < 2, indicative of internal suppression mechanisms. The goal of this project will be to distinguish between the various external drivers of suppression by constraining the timescale and density regimes at which the suppression occurs. To accomplish this, the student will analyze Spitzer observations of a large sample of cluster, infall region, and field galaxies at a variety of redshifts, and compare the observational data to semi-analytic models of galaxy formation.
Getting the Most Out of the Keck Observatory Archive Through Automated Pipelines
Advisor: Chris Gelino
The Keck Observatory Archive (KOA) curates all data obtained with the twin, 10-meter W.M. Keck Telescopes located near the summit of Mauna Kea in Hawaii. KOA's holdings include raw data for all eight of the current instruments as well as two decomissioned ones. Hiding in these 1,700,000+ public science files are tens of thousands of observations of brown dwarfs. Getting the most out of these observations, some of which are unpublished, requires knowledge of how the observations were conducted or a data reduction pipeline (DRP) that can process the data based on the information in the file headers. For this project, the student will build a pipeline in Python for either of the brown dwarf workhorse instruments at WMKO: the high resolution imager NIRC2 and the high resolution spectrograph NIRSPEC. For each of these instruments, there are over 20,000 publicly available science files of observed brown dwarfs. The NIRSPEC pipeline would involve modifying an existing Python DRP (https://github.com/Keck-DataReductionPipelines/NIRSPEC-Data-Reduction-Pipeline) to make it more suitable for brown dwarf studies; a NIRC2 pipeline would involve a new DRP.
A Spectroscopic Survey of Cool White Dwarfs
Advisor: Sergio Fajardo-Acosta
While studying high proper motion objects in the AllWISE and AllWISE2 surveys (Kirkpatrick et al. 2014, ApJ, 783, 122; 2016, ApJS, 224, 36), we re-discovered an object with unusual 2MASS and WISE colors, WISEA 0615-1247, originally thought to be a subdwarf. Upon spectroscopic follow-up in the optical and near-infrared, we discovered that the object is a binary of a late-type dwarf and a cool white dwarf (Fajardo-Acosta et al. 2016, ApJ, 832, 62). The cool white dwarf exhibits metals in its atmosphere, of unusual relative abundances. It is thought that, under ordinary circumstances, metals in these objects are the result of pollution of their atmospheres with accreted material from extant debris disks. Our discovery points out to possible alternative scenarios as the source of these metals.
We are carrying out optical and near infrared spectroscopy of other cool white dwarfs, 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. The goal of these observations is to understand the variety of spectral energy distributions seen in these stars, what their Galactic distribution is, and how often debris disk material is responsible for their atmospheric composition. Of our selected targets, many of which with high proper motions, some are multiple, and therefore we will obtain spectra of late-type dwarf, brown dwarf, and subdwarf companions. These observations may uncover objects of peculiar characteristics, as was the case of WISE 0615-1247.
We expect the graduate student to assist with reduction and analysis of our spectroscopic observations, and with interpretation and publication of results. Since our survey involves various kinds of objects, such as low-mass companions to cool white dwarfs, the graduate student may have some flexibility on the area of research. Spectra of brown dwarf companions, for example, may give a wealth of information on the characteristics of these systems.
The ideal graduate student for this program would have a basic knowledge of white dwarf theory, and familiarity with optical and near-infrared spectroscopy. Knowledge of brown dwarf theory is definitely 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.
