Wyniki wyszukiwania - BazTech

1

Sounding Interiors of Four Pulsating Subdwarf B Stars with Stellar Pulsations

Baran A., Sanjayan S.

Acta Astronomica

|

2023

|

Vol. 73, No. 1

21--34

EN

We present the results of asteroseismic modeling of four pulsating sdB stars KIC 2438324, KIC 2569576, KIC 2991403 and KIC 11159657. We used fully evolutionary models and this is the first attempt of seismic modeling of sdB stars using the MESA models and GYRE. We adopted an already reported list of periods identified with dipole modes. Additionally, we used two spectroscopic parameters, i.e., Teff and log g, and, only for KIC 2438324 and KIC 2569576, we used cluster parameters, i.e., total age and metallicity, to further filter the outcome of matching observed and theoretical pulsation periods. In the case of a spectroscopically constrained approach we derived a unique solution only for KIC 2438324. For two stars we derived unique input parameters except for the hydrogen and progenitor mass, respectively for KIC 2569576 and KIC 2991403. All input parameters except for the convective core and progenitor masses are unique for KIC 11179657. Except for KIC 11179657, our fits, measured by a relative period difference (ΔP/P), are well within 1%. These results sound very promising and more asteroseismic modeling of sdB stars should be done in future.

2

Mode Identification in a Pulsating Subdwarf B Star EPIC 212707862 Observed with K2

Bachulski S., Baran A. S., Jeffery C. S., Østensen R. H., Reed M. D., Telting J. H., Kuutma T.

Acta Astronomica

|

2016

|

Vol. 66, No. 4

455--467

EN

We present an analysis of K2 observations of EPIC 212707862, a pulsating subdwarf B star. We detected 13 significant frequencies from an 81 day run during Campaign 6. Our goal was to find features that could help us to identify pulsation modes. We could not identify any multiplets, which would also have enabled us to precisely derive a rotation period. Based on amplitude modulation we estimated that period to be around 80 days. We found two period-spacing sequences, and successfully identified modal degrees for 11 out of 13 detected frequencies. We assigned six of them to l=1, and another five to l=2. These results will facilitate future theoretical modeling. This star brings to 19 the number of pulsating subdwarf B stars observed with K2. Radial velocities obtained to date and the spectral energy distribution are consistent with EPIC 212707862 being a single hot subdwarf. Analysis of the spectrum gives atmospheric parameters: Teff=28 298±162 K, log g[cm/s2]=5.479±0.025 and log (n(He)/n(H))=-2.752±0.069.

3

Constraining the Hydrogen Envelope Mass of a Pulsating sdB Star KIC 10670103 Through Asteroseismology

Krzesinski J., Blokesz A., Baran A. S., Bachulski S.

Acta Astronomica

|

2014

|

Vol. 64, No. 2

151--165

EN

In this paper we present our study of KIC 10670103, a pulsating hot subdwarf located in the Kepler field. The study is based on three years of data taken by the Kepler spacecraft during Q5-16. Using Fourier analysis, we investigate periodic signals associated with pulsations. Using asymptotic relationships and rotational multiplets we identify modal degrees. The amplitude spectrum appears to be rich in l=1 and 2 multiplets, allowing derivation of a 90 days rotation period for this star. Comparing the pattern of identified gravity mode period spacings with theoretical models, we show that KIC 10670103 is a thick-envelope sdB star.

4

A New Subdwarf-OB Pulsator J23341+4622

Pakštiene E., Qvam J. K. T., Østensen R. H., Telting J. H.

Acta Astronomica

|

2014

|

Vol. 64, No. 4

349--358

EN

A new sdOB variable star, J23341+4622 (SDSS J233406.10+462249.3), was discovered during photometric observations with the Nordic Optical Telescope (La Palma). We found its main pulsation frequency at 7422(±9) μHz with an amplitude of 4.5(±0.5) mma. The star is possibly a complex pulsator, as we found another significant peak at 7759(±11) μHz with an amplitude of 2.0(±0.3) mma and a possible subharmonic of the main frequency at 3508 μHz with an amplitude of 2.3 mma.

5

Detection of Multiplets of Degree ℓ=3 and ℓ=4 in the Subdwarf-B Pulsator KIC 10139564

Baran A. S., Østensen R. H.

Acta Astronomica

|

2013

|

Vol. 63, No. 1

79--90

EN

We present up-to-date results on the short-period sdB pulsator in the Kepler field, KIC 10139564, including 27 months of near continuous photometric data. With this extended dataset we significantly lower the detection threshold, which allows us to detect multiplet components that were missing in our previous analysis based on 15 months of data. We conclude that two regions in the amplitude spectrum of KIC 10139564 contain modes of degree ℓ=3 and ℓ=4, respectively. We also identify many combination frequencies, in both the sub- and super-Nyquist regions, as well as several pulsation modes which show strong frequency or amplitude variability.

6

Mode Identification of Three Pulsating Subdwarf B Stars via Multiplets and Period Spacing

Baran A. S., Winans A.

Acta Astronomica

|

2012

|

Vol. 62, No. 4

343--355

EN

We present an analysis of three pulsating subdwarf B stars residing in short period binaries discovered by the Kepler spacecraft. We followed the analysis presented in Baran. Most of the peaks we detected were assigned to mode degrees and, in the case of the multiplet components, the azimuthal numbers. We confirmed the spin rates for all three stars to be tens of days rather than hours as the binary frequencies may suggest. Using the average period spacings of each object we produced an échelle diagram which shows a common feature at a period of nearly 5000 s. The period spacing between consecutive overtones is quite regular, which confirms that the mode trapping is not significant as previously predicted by the models.

7

Mode Identification in the Pulsating Subdwarf B Star KIC 2697388

Baran A. S.

Acta Astronomica

|

2012

|

Vol. 62, No. 2

179--200

EN

We present our results on mode identification in the pulsating subdwarf B star KIC 2697388 observed with the Kepler spacecraft. We detected 148 frequencies of which five were attributed to p-modes while 122, to g-modes. The remaining 21 frequencies are also likely g-modes. We used multiplets and asymptotic period spacing to constrain degrees of 89 peaks to either l=1 or 2. Using splittings in multiplets we derived the rotation period of this star to be nearly 45 days. The average period spacing between l=1 and 2 overtones are nearly 240 s and 139 s, respectively. Our results show that combining tentative identification based on the presence of multiplets and asymptotic period spacing is indeed useful in mode identification. Mode degree consistently inferred from independent methods make the results reliable and will help to construct accurate models of subdwarf B stars.