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
Short-period pulsating hot-subdwarf stars observed by TESS. II. Northern ecliptic hemisphere
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
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.
Sumanta Sahoo
PhD student, TESS data processor and analyzer.
Jonah Vercher
Graduate student.
Samuel Cope
Undegraduate student.
Jacob Henderson
Undegraduate student.
Brogan Homburg
Undegraduate student.
Rebecca Jolivette
Undegraduate student.
Emmalein Pendley
Undegraduate student.
Damion Quintanilla
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.