Asteroseismology Research Collaboration is dedicated to understanding the pulsating hot subdwarf stars.

About Our Research

The ARDASTELLA collaboration focuses on cutting-edge research projects related to pulsations in hot subdwarf stars (sdB stars). Our primary goal is to deliver groundbreaking discoveries that contribute to the understanding of the structure and evolution of these fascinating celestial objects.

We utilize advanced asteroseismological techniques, which involve studying the oscillations of stars to probe their interiors, much like seismologists study earthquakes to understand Earth's interior. This allows us to gain unprecedented insights into stellar physics.

  • Pioneering asteroseismological studies
  • Analyzing stellar pulsation data
  • Developing new theoretical models
  • Collaborating with international teams
Research Image

What are sdB Stars?

sdB Star Diagram

Subdwarf B (sdB) stars are a class of hot, compact stars that lie on the extreme horizontal branch of the Hertzsprun-Russell diagram. They are characterized by their small size (about 0.1 to 0.2 solar radii), high surface temperatures (20,000 to 40,000 K), and luminosities much lower than typical main-sequence stars.

These stars are evolved objects, having shed most of their hydrogen envelope during their red giant phase. Their cores are composed primarily of helium, which is undergoing nuclear fusion. Understanding their formation and evolution is crucial for stellar population synthesis and galactic archaeology.

The discovery of pulsating sdB stars has opened a new window into their interiors, allowing us to use asteroseismology to probe their internal structure, composition, and dynamics with unprecedented precision.

Meet the Seismoheads

Andy Baran

Andy Baran

Co-head of the collaboration

Observer and data interpreter, including ground telescopes as well as Kepler and TESS space missions.

Mike Reed

Mike Reed

Co-head of the collaboration

Observer and data interpreter, including ground telescopes as well as Kepler and TESS space missions.

Sachu Sanjayan

Sachu Sanjayan

Fresh PhD

Data processor and analyzer.

Samuel Cope

Samuel Cope

Graduate student

Boston Davis

Boston Davis

Undergraduate student

Rebecca Jolivette

Rebecca Jolivette

Undergraduate student

Sophia Keith

Sophia Keith

Undergraduate student

Peter Nemeth

Peter Nemeth

International collaborator

International collaborator of Astroserver.org; supporting spectroscopic observations and data processing.

John Telting

John Telting

International member

International member at Nordic Optical Telescope; supporting spectroscopic observations and data processing.

Roy Østensen

Roy Østensen

International collaborator

International collaborator from Norway; observer and data interpreter, supporting analysis of spectroscopic data.

Recent Papers

Mode identification and period fitting in six pulsating hot subdwarfs

Sahoo S.K., Baran A.S., Németh P., Worters H.L., Pramod Kumar S., Joshi S., Kilkenny D.
2024, Publications of the Astronomical Society of Australia, 41
DOI: 10.1017/pasa.2024.38

Short-period pulsating hot-subdwarf stars observed by TESS. II. Northern ecliptic hemisphere

Baran A.S., Charpinet S., Østensen R.H., Reed M.D., Van Grootel V., Lyu C., Telting J.H., Németh P.
2024, Astronomy & Astrophysics, 685, 65
DOI: 10.1051/0004-6361/202348571

Period variability in the pulsating Extreme Helium stars V652 Her and BX Cir

Kilkenny D., Worters H.L., Baran A.S.
2024, Monthly Notices of the Royal Astronomical Society, 527, 8402
DOI: 10.1093/mnras/stad3544

TIC 378898110: A Bright, Short-Period AM CVn Binary in TESS

Green M.J., Hermes J.J., Barlow B.N., Marsh T.R., Pelisoli I., Gänsicke B.T., Kaiser B.C., Romero A., Amaral L.A., Corcoran K., Grupe D., Kennedy M.R., Kepler S.O., Munday J., Ashley R.P., Baran A.S., Breedt E., Brown A.J., Dhillon V.S., Dyer M.J., Kerry P., King G.W., Littlefair S.P., Parsons S.G., Sahman D.I.
2024, Monthly Notices of the Royal Astronomical Society, 527, 3445
DOI: 10.1093/mnras/stad3412

Short-period pulsating hot-subdwarf stars observed by TESS. I. Southern ecliptic hemisphere

Baran A.S., Van Grootel V., Østensen R.H., Worters H.L., Sahoo S.K., Sanjayan S., Charpinet S., Németh P., Telting J.H., Kilkenny D.
2023, Astronomy & Astrophysics, 669, 48
DOI: doi.org/10.1051/0004-6361/202244888

TESS photometry of the pulsating hot subdwarf star V585 Peg

Reed M.D., Baran A.S., Telting J.H., Østensen R.H.
2023, Monthly Notices of the Royal Astronomical Society, 525, 1342
DOI: doi.org/10.1093/mnras/stad2392

Sounding Interiors of Four Pulsating Subdwarf B Stars with Stellar Pulsations

Baran A.S., Sanjayan S.
2023, Acta Astronomica, 73, 21
DOI: 10.32023/0001-5237/73.1.2

An eclipsing 47 min double white dwarf binary at 400 pc

Munday J., Tremblay P.-E., Hermes J.J., Barlow B., Pelisoli I., Marsh T.R., Parsons S.G., Jones D., Kepler, S.O., Worters H.L.
2023, Monthly Notices of the Royal Astronomical Society, 525, 1814
DOI: 10.1093/mnras/stad2347

Variable Blue Straggler Stars in the Open Cluster NGC 6819 Observed in the Kepler "Superstamp" Field

Guzik J.A., Baran A.S., Sanjayan S., Németh P., Hedlund A.M., Jackiewicz J., Dauelsberg L.R.
2023, The Astrophysical Journal, 165, 188
DOI: 10.3847/1538-3881/acc0f0

A search for variable subdwarf B stars in TESS Full Frame Images III. An update on variable targets in both ecliptic hemispheres - contamination analysis and new sdB pulsators

Sahoo S.K., Baran A.S., Worters H.L., Németh P., Kilkenny D.
2023, Monthly Notices of the Royal Astronomical Society, 519, 2486
DOI: 10.1093/mnras/stac3676

Pulsating hydrogen-deficient white dwarfs and pre-white dwarfs observed with TESS. V. Discovery of two new DBV pulsators, WDJ152738.4−450207.4 and WD 1708−871, and asteroseismology of the already known DBV stars PG 1351+489, EC 20058−5234, and EC 04207−4748

Córsico A.H., Uzundag M., Kepler S.O., Althaus L.G., Silvotti R., Bradley P.A., Baran A.S., Koester D., Bell K.J., Hermes J.J., Gentilo Fusillo N.P.
2022, Astronomy & Astrophysics, 668, 161
DOI: 10.1051/0004-6361/202244198

Filling the gap between synchronized and non-synchronized sdBs in short-period sdBV+dM binaries with TESS: TIC 137608661, a new system with a well-defined rotational splitting

Silvotti R., Németh P., Telting J.H. Baran A.S., Østensen R.H., Ostrowski J., Sahoo S.K., Prins S.
2022, Monthly Notices of the Royal Astronomical Society, 511, 2201
DOI: 10.1093/mnras/stac160

Variable Star Population in the Open Cluster NGC 6819 Observed by the Kepler Spacecraft

Sanjayan S., Baran A.S., Németh P., Kinemuchi K.
2022, Acta Astronomica, 72, 267
DOI: 10.32023/0001-5237/72.4.3

Variable Star Population in the Open Cluster NGC 6791 Observed by the Kepler Spacecraft

Sanjayan S., Baran A.S., Németh P., Kinemuchi K., Ostrowski J., Sahoo S.K.
2022, Acta Astronomica, 72, 77
DOI: 10.32023/0001-5237/72.2.1

Pulsating subdwarf B stars in the oldest open cluster NGC 6791

Sanjayan S., Baran A.S., Ostrowski J., Németh P., Pelisoli I., Østensen R.H., Kern J.W., Reed M.D., Sahoo S.K.
2022, Monthly Notices of the Royal Astronomical Society, 509, 763
DOI: 10.1093/mnras/stab2985

Discovery of 74 new bright ZZ Ceti stars in the first three years of TESS

Romero A.D., Kepler S.O., Hermes J.J., Baran A., Pelisoli I., Oliveira G., Koester D., Klippel T.S., Fraga L., Bradley, P.A., Vučković M., Heintz T.M., Reding J.S., Kaiser B.C., Charpinet S.
2022, Monthly Notices of the Royal Astronomical Society, 511, 1574
DOI: 10.1093/mnras/stac093

Pulsating hydrogen-deficient white dwarfs and pre-white dwarfs observed with TESS. III. Asteroseismology of the DBV star GD 358

Córsico A.H., Uzundag M., Kepler S.O., Althaus L.G., Silvotti R., Baran A.S., Bell K.J., Bischoff-Kim A., Hermes J.J., Kawaler S.D., Provencal J.L., Winget D.E., Montgomery M.H., Bradley P.A., Kleinman S.J., Nitta A.
2022, Astronomy & Astrophysics, 659, 30
DOI: 10.1051/0004-6361/202142153

Pulsating subdwarf B stars observed with K2 during Campaign 7 and an examination of seismic group properties

Reed M.D., Slayton A., Baran A.S., Telting J.H., Østensen R.H., Jeffery C.S., Uzundag M., Sanjayan S.
2021, Monthly Notices of the Royal Astronomical Society, 507, 4178
DOI: 10.1093/mnras/stab2405

Asteroseismic analysis of variable hot subdwarf stars observed with TESS. I. The mean g-mode period spacings in hot subdwarf B stars

Uzundag M., Vučković M., Németh P., Miller Bertolami M., Silvotti R., Baran A.S., Telting J.H., Reed M., Shoaf K.A., Østensen R.H., Sahoo S.K.
2021, Astronomy & Astrophysics, 651, 121
DOI: 10.1051/0004-6361/202140961

A Detection Threshold in the Amplitude Spectra Calculated from TESS Time-Series Data

Baran A.S., Koen C.
2021, Acta Astronomica, 71, 113
DOI: 10.32023/0001-5237/71.2.3

Evolutionary modelling of subdwarf B stars using MESA with the predictive mixing and convective pre-mixing schemes

Ostrowski J., Baran A.S., Sanjayan S., Sahoo S.K.
2021, Monthly Notices of the Royal Astronomical Society, 503, 4646
DOI: 10.1093/mnras/staa3751

Space observations of AA Doradus provide consistent mass determinations. New HW-Vir systems observed with TESS

Baran A.S., Østensen R.H., Heber U., Irrgang A., Sanjayan S., Telting J.H., Reed M.D., Ostrowski J.
2021, Monthly Notices of the Royal Astronomical Society, 503, 2157
DOI: 10.1093/mnras/stab620

A search for variable subdwarf B stars in TESS Full Frame Images II. Variable objects in the northern ecliptic hemisphere

Baran A.S., Sahoo S.K., Sanjayan S., Ostrowski J.
2021, Monthly Notices of the Royal Astronomical Society, 503, 3828
DOI: 10.1093/mnras/stab668

Pulsating hydrogen-deficient white dwarfs and pre-white dwarfs observed with TESS.
I. Asteroseismology of the GW Vir stars RX J2117+3412, HS 2324+3944, NGC 6905, NGC 1501, NGC 2371, and K 1-16

Córsico A.H., Uzundag M., Kepler S.O., Althaus L.G., Silvotti R., Baran A.S., Vučković M., Werner K., Bell K.J., Higgins M.
2021, Astronomy & Astrophysics, 645, 177
DOI: 10.1051/0004-6361/202039202

Detection of a Planet in 2M1938+4603 Revisited

Baran A.S. & Silvotti R.
2020, Research Notes of the Astronomical American Society, 4, 237
DOI: 10.3847/2515-5172/abd31a

PHL 417: a zirconium-rich pulsating hot subdwarf (V366 Aquarid) discovered in K2 data

Østensen R.H., Jeffery C.S., Saio H., Hermes J.J., Telting J.H., Vuckovic M., Vos J., Baran A.S., Reed M.D.,
2020, Monthly Notices of the Royal Astronomical Society, 499, 3738
DOI: 10.1093/mnras/staa3123

A search for variable subdwarf B stars in TESS Full Frame Images I. Variable objects in the southern ecliptic hemisphere

Sahoo S.K., Baran A.S., Sanjayan S., Ostrowski J.
2020, Monthly Notices of the Royal Astronomical Society, 499, 5508
DOI: 10.1093/mnras/staa2991

Alone but not lonely: Observational evidence that binary interaction is always required to form hot subdwarf stars

Pelisoli I., Vos J., Geier S., Schaffenroth V., Baran A.S.
2020, Astronomy & Astrophysics, 642, 180
DOI: 10.1051/0004-6361/202038473

Mode identification in three pulsating hot subdwarfs observed with TESS satellite

Sahoo S.K., Baran A.S., Heber U., Ostrowski J., Sanjayan S., Silvotti R., Irrgang A., Uzundag M., Reed M.D., Shoaf K.A., Raddi R., Vuckovic M., Ghasemi H., Zong W., Bell K.J.
2020, Monthly Notices of the Royal Astronomical Society, 495, 2844
DOI: 10.1093/mnras/staa1337

TESS first look at evolved compact pulsators: Known ZZ Ceti stars of the southern ecliptic hemisphere as seen by TESS

Bognár Zs., Kawaler S.D., Bell K.J., Schrandt C., Baran A.S., Bradley P.A., Hermes J.J., Charpinet S., Handler G., Mullally S.E., Murphy S.J., Raddi R., Sódor Á., Tremblay P.-E., Uzundag M., Zong W.
2020, Astronomy & Astrophysics, 638, 82
DOI: 10.1051/0004-6361/202037470

TESS observations of pulsating subdwarf B stars: extraordinarily short-period gravity modes in CD-28°1974

Reed M.D., Shoaf K.A., Németh P., Vos J., Uzundag M., Baran A.S., Sahoo S.K., Jeffery C.S., Telting J.H., Østensen R.H.
2020, Monthly Notices of the Royal Astronomical Society, 493, 5162
DOI: 10.1093/mnras/staa661

About the existence of warm H-rich pulsating white dwarfs

Althaus Leandro G., Córsico Alejandro H., Uzundag Murat, Vučković Maja, Baran Andrzej S., Bell Keaton J., Camisassa María E., Calcaferro Leila M., De Gerónimo Francisco C., Kepler Souza Oliveira and Silvotti Roberto
2020, Astronomy & Astrophysics, 633, 20
DOI: 10.1051/0004-6361/201936346

K2 observations of the pulsating subdwarf B stars UY Sex and V1405 Ori

Reed M.D., Yeager M., Vos J., Telting J.H., Østensen R.H., Slayton A., Baran A.S. and Jeffery C.S
2020, Monthly Notices of the Royal Astronomical Society, 492, 5202
DOI: 10.1093/mnras/staa144

TESS first look at evolved compact pulsators.
Discovery and asteroseismic probing of the g-mode hot B subdwarf pulsator EC 21494−7018

Charpinet S., Brassard P., Fontaine G., Van Grootel V., Zong W., Giammichele N., Heber U., Bognár Zs., Geier S., Green E.M., Hermes J.J., Kilkenny D., Østensen R.H., Pelisoli I., Silvotti R., Telting J.H., Vučković M., Worters H.L., Baran A.S., Bell K.J., Bradley P.A., Debes J.H., Kawaler S.D., Kołaczek-Szymański P., Murphy S.J., Pigulski A., Sódor À., Uzundag M., Handberg R., Kjeldsen H., Ricker G.R. and Vanderspek R.K.
2019, Astronomy & Astrophysics, 632, 90
DOI: 10.1051/0004-6361/201935395

Asteroseismology of the pulsating helium-atmosphere white dwarf
TIC 257459955

Bell Keaton J., Córsico Alejandro H., Bischoff-Kim Agnès, Althaus Leandro G., Bradley Paul A., Calcaferro Leila M., Montgomery Michael H., Uzundag Murat, Baran Andrzej S., Bognár Zsófia, Charpinet Stéphane, Ghasemi Hamed and Hermes J.J.
2019, Astronomy & Astrophysics, 632, 42
DOI: 10.1051/0004-6361/201936340

High-degree gravity modes in the single sdB star HD 4539

Silvotti R., Uzundag M., Baran A.S., Østensen R.H., Telting J.H., Heber U., Reed M.D. and Vǔcković M.
2019, MNRAS, 489, 4791
DOI: 10.1093/mnras/stz2244

K2 observations of the sdBV + dM/bd binaries PHL 457 and EQ Psc

Baran A.S., Telting J.H., Jeffery C.S., Østensen R.H., Vos J., Reed M.D., Vŭcković M.
2019, MNRAS, 489, 1556
DOI: 10.1093/mnras/stz2209

Two p-mode-dominated subdwarf B pulsators in binaries with F-star companions observed with K2

Reed M.D., Telting J.H., Ketzer L., Crooke J.A., Baran A.S., Vos J., Németh P., Østensen R.H. and Jeffery C.S.
2019, MNRAS, 483, 2282
DOI: 10.1093/mnras/sty3025

Pulsations and eclipse-time analysis of HW Vir

Baran A.S., Østensen R.H., Telting J.H., Vos J., Kilkenny D., Vučković M., Reed M.D., Silvotti R., Jeffery, C.S., Parsons S.G., Dhillon V. and Marsch T.R.
2018, MNRAS, 481, 2721
DOI: 10.1093/mnras/sty2473

Get in Touch

Have questions about our research or interested in collaboration? Feel free to reach out!