We are thrilled that Dr. Alekzander Kosakowski has joined our group as a postdoctoral research associate. Alekzander is an observational astronomer specializing in studies of merging white dwarf binaries as gravitational wave sources and progenitors to stably accreting binaries, massive single white dwarfs, and supernovae. He uses data from large ground-based telescopes to characterize binaries through detailed photometric and spectroscopic analyses. His work makes use of archival data sets from time domain surveys, such as ZTF and TESS, to identify white dwarf systems which show periodic photometric variability on timescales ranging from minutes to hours. Alekzander is the project lead for the “ELM Survey South,” a spectroscopic survey designed to identify and characterize Extremely Low Mass white dwarfs in the southern sky. 

Come work with us as a postdoc in our new research group! Click this link to apply. A complete job description follows.

---

Employee Type:  Postdoc

Position Summary / Primary Purpose of Position:  

The Department of Physics & Astronomy at the University of North Carolina Chapel Hill invites applications for a postdoctoral research scholar to work with Dr. Brad Barlow on numerous projects focused on hot subdwarfs, white dwarfs, and related objects. They will regularly acquire photometry and spectroscopy with the 4.1-m SOuthern Astrophysical Research (SOAR) telescope, reduce/analyze data from SOAR and other facilities, help Dr. Barlow advise undergraduate and graduate research projects, and prepare papers and proposals—among other tasks. The successful candidate will be encouraged to spend a fraction of their time on their own research, especially if such projects utilize data from SOAR. This appointment is for two years, and an additional year is possible contingent on performance and the availability of funding.

All questions regarding this position can be directed by email to Dr. Barlow at bbarlow@unc.edu.

UNC is the founding member of the SOAR consortium and receives an allocation of 61 nights annually on the highly subscribed telescope atop Cerro Pachon, Chile. UNC is also the lead institution for the future Argus Array extremely-wide-field 5m-class time-domain-survey telescope, the Skynet rapid-response array located on four continents, and the Evryscope all-sky survey. UNC has significant high-performance computing resources, including the 17,000-core Longleaf cluster optimized for I/O intensive workloads with dedicated GPU and large-memory partitions.

Applicants should submit the following as part of their application package:

1) a cover letter;

2) curriculum vitae with publication record;

3) a statement of research interests and experience (3-5 pages), including examples of independent projects they would carry out using SOAR data; and

4) contact information for three references.

Letters will only be requested from references once a candidate makes the short list and is invited for an interview. Application review will begin on Aug 1, 2024, and continue until the position is filled.

Minimum Education and Experience Requirements: 

Ph.D. in physics, astronomy, or astrophysics.

Required Qualifications, Competencies, and Experience:

• A history of research and publications focused on hot subdwarfs, white dwarfs, or related objects
• Experience observing with SOAR/Goodman and reducing/analyzing data
• Strong programming skills in Python
• Excellent written and oral scientific communication skills
• Experience effectively mentoring students and working in a team environment

Preferred Qualifications, Competencies, and Experience: 

• Experience running stellar evolution experiments in MESA

Work Location:  

Chapel Hill, NC (remote work possible while successful candidate works on relocation)

The NC Space Grant Consortium awarded our research group a one-year grant to search for new spider binaries. Spider binaries are a class of compact binaries that typically consist of a pulsar (a highly magnetized, rotating neutron star) and a low-mass companion. The intense, high-energy radiation and wind from the neutron star slowly heats up and ablates material from the companion. In time, the orbital period will shorten, and the companion will be consumed. Studies of spider binaries can provide valuable insights into various astrophysical processes, including mass transfer and evolution, the properties and behavior of neutron stars, and high–energy electromagnetic emissions. Such systems are rare, and most have been discovered through X-ray/gamma-ray detections or radio observations of their millisecond pulsars. Due to a series of serendipitous events, our group has discovered one of the closest (and thus brightest) spider binaries currently known using optical photometry instead of radio or high-energy observations. This discovery was made while investigating high signal-to-noise light curves of hot subdwarf binaries — an unrelated type of binary. As the highly irradiated hot spot on the companion rotates in and out of view, the optical flux can vary by up to a factor of ~10 with a light curve shape that mimics those of hot subdwarf reflection effect binaries. Here we propose a series of optical search strategies to uncover and study new spider binaries using data from NASA’s TESS spacecraft, the 4.1-m SOAR telescope, and Skynet.

Congratulations to Zack Hutchens on the successful defense of his Ph.D. thesis “Multiphase Gas in Galaxy Groups in RESOLVE, ECO, and LADUMA” at UNC Chapel Hill! Zack was a member of my undergraduate research group at High Point University and worked on several interesting projects, including the dying pulsations of the sdBV star CS 1246. His Ph.D. thesis (under the guidance of Dr. Sheila Kannappan) focused on developing a group-finding algorithm for the Gas in Galaxy Groups (G3) initiative, enhancing group-finding for the RESOLVE, ECO, and LADUMA surveys. His research provides the first measurement of the HI-halo mass relation without spectral stacking, revealing key insights into galaxy evolution. Additionally, he introduced the Probabilistic G3 (PG3) technique to handle redshift uncertainties, advancing the understanding of HI gas evolution over the past ~9 billion years. Zack will begin work as a postdoctoral student at UNC Asheville this fall!

Hot subdwarfs in close binaries observed from space III: Reflection effect asymmetry from relativistic beaming
Barlow, B.N., Parker, I.*, Smith, B.A.*, Kupfer, T., Schaffenroth, V. 2023, Astronomy & Astrophysics, 686, A126.

Abstract: Detailed studies of hot subdwarf B (sdB) stars with red dwarf (dM) or brown dwarf (BD) companions can shed light on the effects of binarity on late stellar evolution. Such systems exhibit a strong, quasi-sinusoidal reflection effect due to irradiation of the cool companion, and some even show primary and secondary eclipses. For this work, we computed Fourier transforms of TESS light curves of sdB+dM/BD binaries and investigate correlations between the relative amplitudes and phases of their harmonics and system parameters. We show that the reflection effect shape strongly depends on the orbital inclination, with nearly face-on systems having much more sinusoidal shapes than nearly edge-on systems. This information is encoded by the relative strength of the first harmonic in the Fourier transform. By comparing observations of solved systems to synthetic light curves generated by lcurve, we find that the inclination of non-eclipsing systems with high signal-to-noise light curves can be determined to within ≈10° simply by measuring their orbital periods and first harmonic strengths. We also discovered a slight asymmetry in the reflection effect shape of sdB+dM/BD binaries using the relative phase of the first harmonic. From our analysis of synthetic light curves, we conclude the asymmetry results from relativistic beaming of both stellar components. This marks the first time Doppler beaming has been detected in sdB+dM/BD systems. Although advanced modeling is necessary to quantify the effects of secondary parameters, such as limb darkening, the temperature ratio, and the radius ratio on the reflection effect shape, our pilot study demonstrates that it might be possible to extract both the inclination angle and cool companion velocity from the light curves of non-eclipsing systems.

Our research group is hosting the 12th International Conference on Hot Subdwarfs and Related Objects in May 2025! sdOB12 is the 12th edition of a series of biennial conferences started in 2003. These meetings provide experts from around the world the opportunity to discuss results and thoughts on hot subdwarf stars and other related objects. Consider joining us for this event!

Congratulations to Dr. Emily Boudreaux on the successful defense of their PhD thesis “Models of Low Mass Stars as Physical Laboratories” at Dartmouth College! Emily was an incredibly productive member of my undergraduate research group at High Point University from 2015-2019 and actually started doing research with me while still in high school (see a pic of our first day of research together). It was a pleasure working with them at HPU, and it’s been wonderful watching them grow into the outstanding scientist they are today. Congrats, Emily!

Best. Intern. Ever. Big thanks to Fabian Mattig for coming over to North Carolina all the way from Potsdam, Germany, to work with my research group at High Point University for the past six months! Since his first day in the U.S, I’ve been impressed with his enthusiasm for science and work ethic. He’s gathered and analyzed an impressive set of spectra that will surely pave the way for his Master’s thesis and eventual PhD work. I can’t wait to see what the future holds for him. Thanks Fabian, for a fun and productive visit!

SO proud of this guy. Congrats to Dr. Alan Vasquez Soto for successfully defending his PhD dissertation at UNC Chapel Hill! Alan was one of my first undergraduate research students ever at High Point University. We worked on some interesting projects over the years and went on two productive trips down to Cerro Tololo in Chile. Watching him grow from a first-year undergrad to the scientist and instrumentalist he is today has been an honor!