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Currently, we are working on research projects related to pulsations in hot subdwarf stars. The projects will surely help deliver a number of great discoveries published in papers of international standing. We hope that these results will finally allow us to make headway in understanding the precise structure and evolution of these enigmatic objects.

sdB stars

The stars that are spectroscopically classified as subdwarf B (sdB) stars are found in the Hertzsprung-Russell diagram between the main sequence and the white dwarf cooling track. They are compact stars and the majority are located on the blue extension of the horizontal branch, earning them the designation extreme horizontal branch (EHB) stars. As such, they are understood to be the helium burning cores of low-mass stars (0.8 – 1.5 M) that ignited helium through the core-helium flash when their cores reached the required mass of 0.47M. They have effective temperatures between 20000 and 40000K and the surface gravities (in logarithmic cgs units) between 5.0 and 6.0. Another channel to reach that location is through more massive progenitors (1.5 – 2.5 M), which do not experience the helium flash, however more hydrogen envelope must be removed.

While their helium cores are effectively burning helium into carbon and oxygen, their hydrogen envelopes have insufficient mass to sustain significant shell-hydrogen burning unlike the normal horizontal branch and red clump stars. For the envelope to become this thin, some process must have stripped off the majority of the mass during or immediately after the first red-giant branch stage.

At least half of sdB stars are found to be in binaries, but a significant fraction are definitely single in the sense that there is no object found close enough to have interacted during their evolution. Therefore, the evolutionary channels leading to sdB stars must explain both populations. In case of the binaries, the mass transfer is a natural way to remove the envelope from the sdB progenitor, while the single sdBs may be mergers of two stars.

In 1996 Dave Kilkenny and his group discovered the first pulsating sdB (sdBV) star and this has opened the way to study their interiors using asteroseismology. The pulsation periods of sdBV stars are found to be quite short, between 3 and 10 minutes. The same year, Stephane Charpinet and his group calculated theoretical models of sdBV stars and explained the flux variations as pressure modes (and later also as gravity modes) driven by the kappa-mechanism, which works on the Z-bump.

Nowdays, our Ardastella group is trying to implement the MESA code to calculate fully evolutionary models all the way to EHB stage. Next, we will calculate the eigenmodes to match with those detected in our space data. In fact … this step is being done now. This is the first time fully evolutionary models of sdB stars are used for asteroseismology and will serve as a comparison to the already available results from static models.

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, accepted
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., Brown A., Littlefair S.P., Hegedus R., Baran A., Breedt E., Dhillon V.S., Dyer M.J., Green M.J., Kennedy M.R., Kerry P., Lopez I.D., Romero A.D., Sahman D, 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., Amaral L.A., Uzundag M., Bognár Z., Bell K.J., VanWyngarden M., 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., Silvotti R., Althaus L.G., Koester D., 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

Seismoheads


Mike Reed

Co-head of the group

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

 

 

 


Andy Baran

Co-head of the group

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

 

 

 


Sachu Sanjayan


Fresh PhD. Data processor and analyzer.

spacentity.org/

 

 

 


Sumanta Sahoo


PhD student, TESS data processor and analyzer.


Jonah Vercher

Graduate student.


Samuel Cope


Undegraduate student.

 

 

 


Brogan Homburg


Undegraduate student.

 

 

 

 


Rebecca Jolivette

Undegraduate student.


Peter Nemeth

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


John Telting

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


Roy Østensen

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