Southampton Projects

Submitted by: 
Konstantina Anastasopoulou

Studying massive stars in X-rays is crucial for understanding the extreme physical processes and environments associated with these stellar giants. X-ray observations reveal shocks embedded in the winds of single stars or produced in the wind-wind collision zones of massive star binaries. Understanding these phenomena across different types of massive stars provides valuable insights not only for the final stages of stellar evolution but also for how these phenomena influence the dynamics and evolution of their surroundings, including the interstellar medium and star formation. Specifically, the massive star cluster Westerlund 1 is ideal for studying a large, coeval, and diverse population of massive stars. It is the most massive star cluster known in the Milky Way, it is the closest star cluster to the Sun belonging to the super-star clusters family, and it hosts the largest and most variegated population of massive stars found in a single cluster (166 so far).

Our team has obtained a very deep X-ray observation of Westerlund 1 using the Chandra Space Telescope. The unprecedented high angular resolution of Chandra, has enabled the detection for the first time in X-rays of an impressive number of approximately 6000 stars. Matching with optical catalogues a large number of massive stars (~100) have been identified. However, these catalogues are not complete and we expect that many of the new X-ray detections correspond to unknown massive stars particularly of late O and B spectral type. The student is expected to identify the missing massive star component in Westerlund 1, by utilising the high sensitivity of the Chandra observations in combination to Gaia data, to construct a complete catalogue of massive stars, and to measure the X-ray properties (colours and spectra) of the newly identified massive stars. This will provide valuable insights to our knowledge of the X-ray production mechanism for massive stars particularly for the less explored in the X-rays late O and B stars.

The student will have the opportunity to be part of the EWOCS (Extended Westerlund 1 and 2 Open Clusters Survey) collaboration which involves more than 50 scientists from all over the world, and is currently based on a 1Msec Chandra/ACIS-I Large Program (P.I. M.Guarcello) and two Cycle 1 and 2 JWST MIRI and NirCAM programs (P.I. M.Guarcello).

Advisors: Konstantina Anastasopoulou (CfA), and supported/mentored further by other EWOCS members: led by Mario Guarcello (Observatory of Palermo, Italy), incl. Jeremy Drake (Lockheed Martin), Rafael Martinez-Galarza (CfA), Kristina Monsch (CfA), Joshua Bennett Lovell (CfA)

Additional information:
https://westerlund1survey.wordpress.com/

Will be supported by the following grants:
JWST Westerlund 1

Submitted on:
June 3, 2024

Submitted by:
Rosanne Di Stefano

Existing X-ray archives contain a wealth of data that have not yet been fully explored. Among them are short time-scale variations during individual exposures. Why search for short-duration events? Short-duration events provide unique information about physical systems and the processes occurring within them. Phenomena from transiting planets and moons, to gravitational self-lensing by black holes or neutron stars with bright, compact companions, to flares on neutron stars, and more, can all be identified as distinctive short-duration events in X-ray light curves.

We are conducting a systematic investigation of the rich set of light curves collected by space missions to search for and study X-ray events of short duration. Our study includes all bright X-ray sources (XRSs) listed in the catalogs of Chandra and XMM-Newton, to identify short events. In addition, we conduct follow-up analyses with data from other missions, such as Swift, ROSAT, and eRosita, to determine whether similar short-duration events are present. Counterpart information is searched for in all available ground- and space-based data bases. The most intriguing events are targeted for detailed theoretical modeling.

The student selecting our project will be able to choose from a variety of subprojects as the topic of their thesis. For example, a key element of our research is to discover and classify short events. Methods that include machine learning will be applied and will lead to interesting discoveries. Alternatively, modeling individual events to determine their true natures requires theoretical work. Another type of potential project is to establish population characteristics for the variety of phenomena that produce short X-ray events. The student will be joining a supportive group, the expertise of whose members covers a broad range of astrophysics. Our group has already discovered the first candidate for an extragalactic planet, and has found evidence of an X-ray triple in a globular cluster.

Will be supported by the following grants:
Existing NASA grant

Submitted on:
June 3, 2024

Submitted by
Dong-Woo Kim

Multi-wavelength studies of X-ray sources allow for discovering unexpected and paradigm-changing sources, such as X-ray bright optically normal galaxies (XBONGS), which are supermassive black holes hidden behind massive layers of dust (see press release1). Compared with the previous version, the improved Chandra Source Catalog (v2.1) will have 29% more X-ray sources with more accurate source positions. In this project, the student will explore the new Chandra X-ray sources cross-matched with optical/IR/UV/radio surveys using tools of machine learning to accomplish the following goals:

• Improve the separation between different types of objects (stars, galaxies, XBONGs, AGNs, and QSOs) in the multi-wavelength parameter space of properties. This will be achieved using unsupervised and supervised machine learning techniques and will improve on current methods that rely on linear separations.
• Find the most extreme relationships among multi-wavelength properties that will unveil new types of objects, such as XBONGs, by systematically applying an anomaly detection algorithm to the cross-matched catalog. Methods include unsupervised random forest and dimensionality reduction.

The student will get acquainted with AI software tools, the physics of extreme accretion events in the universe, as well as data science techniques for exploring large datasets. Knowledge of Python programming is preferred, but previous experience in astronomy and astrophysics is not required. The ASTRO-AI team2 at the Center for Astrophysics Harvard and Smithsonian will support this project, when necessary, e.g., in applying the essential s/w tools and interpreting the outputs.

Additional information:

• https://chandra.harvard.edu/photo/2023/xbongs/index.html
• https://astroai.cfa.harvard.edu/

Will be supported by the following grants:
Chandra grant

Submitted on:
June 1, 2024

Submitted by
Qian Yang

Quasars are supermassive black holes (SMBHs) actively accreting material. They are known for their variability. Not only does their brightness change, but also the shape of their continuum emission and the strength of broad-line emission. Such changes reveal a lot of otherwise inaccessible information about the structure and dynamics of the region surrounding the SMBH.

There is a population of extremely variable quasars, known as changing-look quasars, which switch states between active and inactive, transitioning from normal galaxies to actively accreting states. This project will analyze a large sample of spectra from SDSS to identify changing-look quasars, and to test whether they are a unique quasar species, or simply the most highly variable quasars.

For the interested student, we will be applying Python-based spectral fitting pipelines to explore the properties of changing-look quasars in the context of the big picture. Candidate topics include investigations of the occurrence rate of changing-look phenomena, black hole properties and their relationship to their host galaxies, and the growth of SMBHs over cosmic time. We will discuss these and other options to hone in on a specific project based on the students particular interests.

Will be supported by the following grants:
Chandra grants

Submitted on:
May 31, 2024

Submitted by
Amy Gall

One of the most surprising results from the last 30 years of high-resolution, high-energy spectroscopy of stars is the large range in electron densities observed in stellar coronae. Density studies can provide clues to the coronal heating process and generally rely on a few spectral lines from a couple of ions. Bright Fe-L lines, from n 3 to n = 2 transitions, can provide additional diagnostics of electron density and help fill in the emission measure distributions, e.g. the amount of material as a function of electron temperature, to provide a better understanding of stellar structure and heating. However, Fe-L lines are currently underutilized due to concerns about the accuracy of the atomic data underlying astrophysical models.

For this laboratory-based project, the student will make highly accurate wavelength measurements of Fe-L transitions to improve the fits, identifications, and inferred values (density) derived from this complex and diagnostically rich region of stellar spectra. Fe-L emission will be created in an Electron Beam Ion Trap (EBIT), a small-scale device that produces a plasma with temperatures and densities similar to the solar corona. Targeted Fe-L wavelength measurements will be made with a high-resolution, Johann-type crystal spectrometer. The student will set-up and test the spectrometer, collect and analyze data, and compare results with the current atomic data used in astrophysical models.

Will be supported by the following grants:
Chandra grant

Submitted on:
May 31, 2024

Submitted by
Dan Schwartz

Galaxies grow by mergers, and since each has a supermassive black hole (SMBH) at its center these tend to sink to the center of the merged galaxy. If both SMBH are accreting material they will appear as Active Galactic Nuclei (AGN) or quasars. Finding such systems is important to assess how galaxies form and evolve, and because the SMBH pairs are thought to form bound binary pairs and eventually merge, emitting powerful gravitational waves. Examples of dual AGN are known with separations from a few kpc to tens of kpc. However at redshifts greater than even a few tenths, they are difficult to find with smaller separations.

Varstrometry (from VAriable aSTROMETRY, Shen, Y. et al. 2019, ApJL, 885) exploits the position jitter of an unresolved source to deduce that the system is really composed of two variable sources. As those sources vary randomly and independently, their unresolved position is measured to be at their center of flux. Quasars are ubiquitously variable in X-rays and therefore natural targets for such an investigation. This project can proceed along one of the following lines of investigation:

1. Use multiple Chandra observations of many AGN for which other nearby sources can provide an astrometric reference, to search for duality at separation scales of a few hundred parsec to a few kpc.
2. Exploit the amplification resulting from gravitational lensing to search for separations of a few tens pc to a few kpc.

Will be supported by the following grants:
Chandra grant

Submitted on:
May 31, 2024

Submitted by
Adam Foster

Accurately measuring emission in line rich spectra (e.g. stars) requires an accurate model of the intensity and wavelength of the light, the shape of the emission line, and the response function of the instrument. Work with line rich spectra in Chandra has implied that the wings of strong lines may not be accurately represented, while experimental work at electron beam ion traps has demonstrated the importance of accurately modeling the lines shape when searching for blends. Accurate modeling of these line wings sounds like it will have only a minor effect on the spectra, but will in reality have a major effect on the implied elemental abundances of the whole range of plasmas by changing the continuum level in the fits, with potential impacts on observations of supernovae and nucleosynthesis models.

In this project, you will approach the line shape issue from two directions: first, by looking at the extensive Chandra dataset from Capella you will study whether changing the line shape in the response will better model the wings of the emission. This will then be applied to other data sets to test whether the new emission is reasonable. Secondly, you will changethe line shape within modeling tools to study the impact of correct models - Voigt profiles instead of Gaussians - on fits to stellar spectra.

Will be supported by the following grants:
NASA ADAP grant

Submitted on:
May 31, 2024

Submitted by
Adam Foster

Interpretation of all high resolution spectroscopy from current and future missions requires accurate knowledge of a large selection of atomic data, from wavelengths to transition probabilities to collision strengths. Currently, nearly all of this atomic data is created using theoretical calculations folded through plasma models to create spectra these are then compared with observed spectra to imply the astrophysics occurring.

However, the accuracy and completeness of many atomic data calculations remains unclear at best. While wavelengths are measured for the strongest lines, nearly all other atomic data are theoretical. In this project, you will use machine learning autoencoder techniques with Chandra and XRISM observations of galaxy clusters and stars to optimize the atomic structure calculations themselves. This will lead to significant improvements to the atomic data and therefore aid in analysis of more complex spectra across the entire field.

Will be supported by the following grants:
NASA ADAP grant

Submitted on:
May 31, 2024

Submitted by
Kristina Monsch

Protoplanetary disks are rotating accumulations of gas and dust surrounding young stars and are the birthplaces of planets, moons, and smaller bodies that make up planetary systems. By studying protoplanetary disks, we can gain critical insights into the processes of planet formation, the conditions that lead to the development of planetary systems, and the chemical and physical environments of early star systems. Investigations into these disks help us understand the diversity of exoplanetary systems, the potential for habitability, and the origins of our own solar system.

Draculas Chivito (IRAS 23077+6707) is a recently discovered, edge-on protoplanetary disk, which appears like a giant cosmic butterfly. It is the largest known protoplanetary disk in the sky, both in terms of angular and physical size, spanning up to 2000 au in radius. Draculas Chivito is so massive that its likely able to form multiple Jupiter-like gas giants over the wide extent of its disk, and thus provides a golden opportunity to understand planet formation in planet-forming disks of extreme size.

Our team has recently obtained a suite of radio and (sub-)mm observations of this enigmatic system, including data from the Submillimeter Array (SMA), the Northern Extended Millimeter Array (NOEMA) and the Very Large Array (VLA). The student will use these data to extract source fluxes, and fit the thermal and non-thermal emission spectra of Draculas Chivito. Such spectra enable constraints on the dust composition, temperature distribution, and disk-star ionization interactions, which are essential for understanding the processes of planet formation and disk evolution. This comprehensive analysis enables the validation and refinement of theoretical models, providing deeper insights into the mechanisms shaping planetary systems. It is anticipated that at least one professional journal paper should result from the work that the student will be encouraged to lead. Further, the student will be able to lead an observing proposal, if they are interested.

Advisors: Kristina Monsch, Joshua Bennett Lovell, David Wilner

Additional information:

https://www.cfa.harvard.edu/news/giant-cosmic-butterflys-nature-revealed

https://sites.google.com/site/kristinamonsch/home

Will be supported by the following grants:
TBD

Submitted on:
May 31, 2024

Submitted by
David Wilner

The Atacama Large Millimetre/submillimetre Array (ALMA) has revolutionized our view of planet formation, having provided detailed images of hundreds of disks in which planets are forming and dozens more where planet formation has all-but ended, where planet--disk interactions can be studied in detail. Debris disks -- rings of dusty material around main-sequence stars -- provide testbeds to study the evolution of planetary systems over 10s to 1000s of Myrs, and therefore new views on how planetary systems, and our own Solar System, develop.

A key outcome of planet-disk interactions is the formation of asymmetric, eccentric disks resulting from planetary gravitational perturbations. These asymmetries can be characterized in detail and used to infer the properties of the unseen planets that shape the disks. So far, three eccentric debris disks have been carefully modelled, but there are about a dozen more systems where high-resolution ALMA data are available to provide constraints on disk eccentricities. We are offering a one year Southampton student project to work with cutting edge-models to systematically fit the eccentricities of these systems, and, for the first time, derive the distribution of eccentricities in the population of the brightest and best-resolved debris disks. This work will offer a new and fundamental view of typical planetary architectures in the outer regions of exoplanetary systems, and will provide the student with hands-on experience with ALMA data and advanced modeling techniques. The student will be supported in the write-up of the project results for submission to an academic journal.

Advisory team: Joshua Lovell, David Wilner, Sean Andrews.

Additional information:

https://www.almaobservatory.org/en/home/

https://astrojlovell.github.io/

Will be supported by the following grants:
Student AAS meeting travel will be supported by SAO RG Division funds.

Submitted on:
May 31, 2024

Submitted by
Rafael Martinez-Galarza

The first 10 million years of a stars life typically occur whilst these remain bound to their parent clusters. Moreover, this time span is likewise critical for the formation and development of planets, which are born in protoplanetary disks. Protoplanetary disks are understood to disperse on comparable timescales, whereby these leave behind the planets that formed with them. But how these disks evolve -- on what timescales, and how this relates to the presence of nearby strongly radiating massive stars -- remain open questions, of special importance in our growing understanding of how exoplanets are born and develop in their early stages.

JWST is now providing breakthrough insights into these questions with new phenomenal detail resolving the physical structures associated with parental stellar clusters, and offering unprecedented photometric sensitivity to dust excesses associated with young stars, the signposts of their protoplanetary disks. Our team has access to brand new, unpublished JWST MIRI (Mid Infrared Instrument) data of the nearby, young, massive open cluster, Westerlund-2. We are offering a unique opportunity for a Southampton student to 1) learn how to use and run the JWST MIRI calibration pipeline to produce MIRI images, 2) conduct photometric extractions of stellar emission to hunt for the presence of protoplanetary disks within the cluster, and 3) analyse disk detections in the context of their locations and ages of their host stars. We seek to answer where in the cluster protoplanetary disks have formed, and whether these have preferentially dispersed in locations closer to the clusters massive stars. The student will join the international EWOCS (Extended Westerlund Open Cluster Survey) collaboration, and be mentored by a dedicated team of local CfA members. The student will be encouraged and supported to write up their results in a professional academic journal.

Advisors: Rafa Martinez-Galarzo, Kristina Monsch, Joshua Bennett Lovell (CfA), and supported/mentored further by other EWOCS members (led by Mario Guarcello, incl. Jeremy Drake, Konstantina Anastasopoulou.

Additional information:

https://westerlund1survey.wordpress.com/simulated-miri-images/

Will be supported by the following grants:
JWST grant

Submitted on:
May 31, 2024

Submitted by
James Steiner

NICER is the premier soft X-ray timing instrument on the X-ray sky, and operates from the International Space Station. NICER is amassing an unprecedented archive of X-ray spectral-timing data on the brightest objects in the X-ray sky -blackholeX-ray binaries. Several of these objects are persistent, but the vast majority undergo year-long outbursts which are marked by transitions through a pattern of spectral-timing states. During these outbursts, blackholes launch relativistic jets, emit powerful winds, and produce dynamic humming patterns known as quasi-periodic oscillations (QPOs).

NICER has produced tens of thousands of observations of these systems, often consisting of near-daily snapshots during an outburst. For the interested student, we will be applying (python-based) machine-learning / AI algorithms to explore the properties of these rich X-ray binary systems. Candidate topics include investigations of outflowing winds, determining black-hole spins and inclinations, spectral and QPO cross-connections, or classification algorithms to automatically determine spectral state or distinguish between black-hole and neutron-star systems. We will discuss these and other options to hone in on a specific project based on the students particular interests.

Will be supported by the following grants:
NICER / NuSTAR GO

Submitted on:
May 30, 2024

Submitted by
Mojegan Azadi

Deep in the heart of every large galaxy is a supermassive black hole, a million to a billion times more massive than our Sun. The strong gravitational force of that supermassive black hole drags the nearby gas and stars into the very center of the galaxy, releasing tremendous amounts of energy. As a result, the galaxy nucleus radiates at all wavelengths (from radio to X-rays and gamma rays). In some cases, relativistic jets emerge from the vicinity of the supermassive black holes, creating complex radio-emitting structures extending over tens of thousands of light years. Active supermassive black holes are among the most luminous objects in the Universe.

The impact of supermassive black holes on galaxy evolution is a longstanding, unresolved issue that astronomers have been trying to address for several decades. For example, the triggers for supermassive black hole activity and the impact of that activity on host galaxies star formation are not well understood. To address these issues, our project seeks to characterize the fundamental properties of galaxies hosting supermassive black holes identified via X-ray imaging with the Chandra X-ray telescope. Crucially, X-ray imaging, which is largely unaffected by gas and dust absorption, offers a reliable method for pinpointing active black holes.

The goal of this program is to analyze the Chandra Source Catalog, comprised of thousands of X-ray detected sources, to identify the active supermassive black holes. The student will be involved in several related investigations, including cross-matching the X-ray sources with counterparts at other wavelengths, including radio, sub-millimeter, infrared, visible, and UV data available from other space or ground-based telescopes. Additionally, the student will be trained to use state-of-the-art tools (including galaxy spectral energy distribution modeling) to estimate the properties of galaxies and supermassive black holes, carry out detailed statistical analysis of the results, and write up the results in an article to be submitted to a prestigious astronomical journal.

This project is part of the Unified Multiwavelength Broad Research Center Exploring AGN (UMBRELA). UMBRELA explores active galaxies and their central supermassive black holes across a broad spectrum of wavelengths and emphasizes mentoring students, particularly in developing expertise across the electromagnetic spectrum, encompassing both theory and observation. The student joining this project will have access to all the expertise and receive support and mentorship from experienced members of UMBRELA.

Additional information:

https://cxc.cfa.harvard.edu/csc/

https://umbrela.cfa.harvard.edu/

Will be supported by the following grants:
TBD

Submitted on:
May 30, 2024

Submitted by
Sylvain Korzennik

The scientific goals are to use state-of-the-art inversions for the solar internal rotation and/or internal structure, and their variation with solar activity using inversion techniques and optimal fitting methodologies.

One possible avenue of research is to improve the current fitting method, while alternative options are to work on traditional inversion techniques or innovative inversion techniques based on machine learning. The scientific goal is to study the tachocline and its variation with the solar cycle.

The solar tachocline is a narrow region where the solar rotation transitions from solid-body in the inner regions to a differential profile in the outer regions. Its presence in the Sun remains a puzzle both from a theoretical and observational perspective, not unlike the fact that the solar rotation is not constant on cylinder as initially predicted. This transition layer was not anticipated prior to its detection by helioseismology and its properties are key to explain how and why the Sun maintains a tachocline, yet there is no definite observational constraints that favor one model of the tachocline over another.

Such work will directly contribute to our understanding of the origins of the Suns activity (key science goal 1 of the Heliophysics Decadal Survey) and further key science goal 4 by contributing to our understanding of the solar dynamo, and therefore similar dynamos in stars, and specifically solar-like stars. And it will draw extensively from various data set: HMI observation from SDO(12+ years), MDI observations from SOHO (14+ years) and GONG observations (25+ years).

Additional information:

http://hmi.stanford.edu/

https://gong.nso.edu/

Will be supported by the following grants:
Existing NASA grants

Submitted on:
May 30, 2024

Submitted by
Martin Elvis

The return of humans to the Moon by 2028, with permanent bases planned for ~2035, has spurred astronomers to come up with ideas for new telescopes that take advantage of the special environments on the Moon. One of these is to use the coldest of the cold traps near the lunar poles for a far-infrared telescope working at ~25K. At these temperatures the black body emission of the telescope and its surroundings will be pushed out to long wavelengths so that the far-IR will become far more sensitive. Such a telescope could do cosmology with the cosmic microwave background, study the first galaxies and black holes, and look for new biosignatures from exoplanets. But others will want to use these permanently shadowed regions (PSRs, Paige et al. 10.1126/science.1187726), particularly for water mining. Astronomers need to build their case for protecting some of these areas as sites of extraordinary scientific importance. The IAU Working Group on Astronomy from the Moon is gearing up to do so.

This project will create a map of the possible sites, will catalog their properties, and create an initial ranking as input to the IAU WG. We expect to publish the results in RASTI, as we did with a previous project (Le Conte et al. 2023RASTI...2..360L).

The project will be jointly overseen by Drs. Martin Elvis and Magorzata Sobolewska.

Additional information:

https://www.iau.org/static/science/scientific_bodies/working_groups/342/wg-342-triennial-report-2021-2024.pdf

Will be supported by the following grants:
Chandra grant

Submitted on:
May 30, 2024

Submitted by
Scott Randall

Recently, radio observations have identified a new class of diffuse radio sources characterized by their very steep radio spectra. These ultra-steep spectrum (USS) sources are often found in galaxy clusters, particularly in merging clusters. They often have irregular morphologies, and can be up to megaparsecs in size (on the order of the size of clusters themselves). The nature of these sources is unclear. They may arise from particle acceleration at merger shock fronts (radio relics), from adiabatic compression of fossil non-thermal electron populations (radio phoenixes), associations of old radio plasma left over from a previous AGN outburst (AGN relics), or some mix of these three.

This project will involve the analysis of an XMM-Newton X-ray observation of a USS host cluster. Image analysis, as well as spectral analysis used to construct thermodynamic maps, of the diffuse intracluster medium (ICM) will be used to constrain the dynamical state of the cluster, and correlate X-ray structure with the USS radio source. This will, in turn, provide information on the possible formation scenarios of USS sources.

Will be supported by the following grants:
XMM grant

Submitted on:
May 30, 2024

Submitted by
Yuexin Zhang

During outburst, black-hole X-ray binaries (BHXRBs) exhibit variability over a wide range of timescales, offering a unique insight into the accretion-ejection processes and the underlying physics of these sources. Even still in its infancy, the modelling of accretion flows holds the promise of constraining the geometry around and of BHs, such as disk truncation, electron temperature, and BH spin. In particular, the evolution of the disk inner radius of the accretion disk at the viscous timescales appears to hold crucial information about the processes that drive accretion onto the BH and their powerful ejections along relativistic jets.

Using data from NICER and NuSTAR, we propose a project to investigate a recently discovered black-hole X-ray transient, Swift J1727.8-1613. This transient exhibited an extraordinarily bright outburst, offering promising opportunities to constrain the accretion flow and establish its relation with the onset/quenching of relativistic outflows. We will employ the state-of-art relativistic disk reflection model or disk continuum model to study this source and measure key parameters.

Our discoveries will provide a first full description of the accretion-ejection zones predicted theoretically, a clear picture of the physical components present in Swift J1727.8-1613 and their correlated evolution across outburst. Ultimately, our results will significantly advance our understanding of the physics of mass accretion and ejection in these fascinating objects.

Submitted on:
May 30, 2024

Submitted by
Paul Green

Carbon is produced in the cores of stars, and is brought to the surface in pulsations on the asymptotic giant branch (AGB). We have just completed a massive survey for carbon (CO) stars across the Milky Way, using XP spectra from the Gaia mission. Bizarrely, a hefty fraction of those carbon stars are dwarfs, not AGB stars. These dC stars were polluted by winds from an AGB companion, whose white dwarf remnant still orbits the dC. Some orbits are so close that the dC must have been subsumed within the AGB envelope (common envelope evolution). Such close WD/dC pairs can be discovered by their strong variability in TESS, ATLAS, or ZTF. This new project would study the lightcurves to find close WD/dCs, measure their radial velocity variability to contrain orbits, and perhaps find the first sample of dCs in eclipsing binary systems, which would enable the first dC mass measurements. Alternate (or additional) Gaia-related projects include finding new WD/dCs directly from their XP spectra. We may also attempt to find dS stars (polluted dwarfs with C~O) which should exist, but have never been found.

The project would be co-mentored by Ben Roulston, faculty at Clarkson University.

Additional information:

https://ui.adsabs.harvard.edu/abs/2021ApJ...922...33R/abstract

https://hea-www.harvard.edu/~pgreen/

Will be supported by the following grants:
Several Chandra grants

Submitted on:
May 29, 2024

Submitted by
Steven Saar

The quest to find Earth analogs (Earth mass planets in their stars habitable zones) is major goal of modern astronomy. Precise radial velocities (RV) are required to determine planet masses. Progress has been hindered though, by puzzling noise sources which prevent RVs from being measured to much better than about +/- 1 m/s. Since the Earth wobbles our Sun by +/- 10 cm/s, this is a problem Magnetic and hydrodynamic processes on the parent stars themselves seem responsible for this noise. Some of these (e.g., magnetic spots and plages) have already been confirmed as noise sources and correction methods have been devised. This project aims to identify, and test models for removing some more subtle magnetic phenomena: sunspot moats, active region inflows, and flares. We will do this using high resolution data from the nearest, best understood star: our own Sun. If we are successful, we will be one step closer to bringing true exo-Earths within range of our detection and study.

Will be supported by the following grants:
NASA grants

Submitted on:
May 28, 2024

Submitted by
Kim-Vy Tran

Gravitational lensing has matured into a powerful cosmic tool for exploring a wide range of astrophysical phenomena such as multiply imaging a single supernova, identifying the highest redshift galaxies, and mapping dark matter distributions. With upcoming all-sky surveys, we are at the brink of a revolution where deep high resolution imaging of vast cosmological volumes is becoming widely available.

I currently lead the ASTRO 3D Galaxy Evolution with Lenses (AGEL) Survey (Tran et al. 2022) to deliver a benchmark sample of new gravitational lenses that can be observed by both northern and southern hemispheres to obtain high quality follow-up with upcoming Adaptive Optics and space telescopes. The AGEL observations include an ongoing Hubble Space Telescope program to image 500 strong lenses, extensive ground-based spectroscopy of the deflectors and sources, and complementary multi-wavelength observing campaigns to capture the interplay between gas and stars.

Potential thesis research projects include measuring the dark matter profiles of the foreground deflector halos mapping the Circum-Galactic Medium associated with the foreground deflector quantifying the changing conditions of the Inter-Stellar Medium of the background lensed sources and measuring the Hubble constant for a subset of compound lenses that have two sources at different redshifts.

About me: I have graduated 5 PhD students, served on 15 PhD committees, and supervised 30+ undergrads in research including Honors theses. I develop and support professional development opportunities for early career researchers as part of my current role as the Associate Director for Internal Relations at the CfA.

Additional information:

https://www.kimvytran.org/

Will be supported by the following grants:
STScI grants

Submitted on:
May 22, 2024

Submitted by
Joseph Hora

Background: Sgr A, the central supermassive black hole (SMBH) of our Galaxy, is more than 100 times closer than any other massive black hole and therefore can be studied in far greater detail. Sgr As accretion flow is detected in the radio, submm, near-IR, and X-ray regimes and it is variable at all wavelengths. The relatively rapid (minutes to hours) fluctuations and temporal correlations between the NIR, submm, and X-ray indicate that the variable emission originates in the innermost regions of the accretion flow, not far outside the event horizon. Observations with GRAVITY/VLT have detected positional and polarization changes consistent with emission from a hot spot just outside the innermost stable circular orbit of the SMBH. Recent observations from ALMA, collected in concert with the Event Horizon Telescope, also show polarization variations, including loops that seem to trace a second instance of an orbiting hot spot. The emission and accretion mechanisms in this critical regime can be understood via targeted study of the variability.

Recent modeling has suggested two possible scenarios to explain the emission: magnetic reconnection near the event horizon, or secondary magnetic reconnection in the flux tube/hot spot ejected by the event horizon reconnection layer. The questions we will answer are: what is the origin and energy distribution of the non-thermal electrons? What are the variable SED properties from the submm to the NIR and X-ray? Are there delays between the emission from different wavelengths, and can they be explained by expansion or the reconnection mechanisms? Do bright flares have a different physical nature than the low level variability? And on the side of emission models: Are single-zone models adequate? Can we differentiate between the two reconnection scenarios?

We have obtained simultaneous JWST/MIRI, Chandra, and ALMA/SMA observations of Sgr A in April 2024. The project will include reducing and analyzing these datasets to determine the emission mechanisms at work.

Additional information:

https://lweb.cfa.harvard.edu/irac/gc/

https://ui.adsabs.harvard.edu/abs/2022ApJ...931....7B/abstract

Will be supported by the following grants:
JWST grant (expected to start in summer 2024)

Submitted on:
May 21, 2024