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  • 1
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    Online Resource
    A review of seismic observations of Kepler and K2-Observed sdBV stars
    Walter de Gruyter GmbH ; 2018
    In:  Open Astronomy Vol. 27, No. 1 ( 2018-07-18), p. 157-166
    Details
    In: Open Astronomy, Walter de Gruyter GmbH, Vol. 27, No. 1 ( 2018-07-18), p. 157-166
    Abstract: This paper reviews recent seismic findings from Kepler and K2 data. Using three years of short cadence Kepler (K1) data, it is possible to examine time evolution of pulsations in an unprecedented way. While K2 observations are shorter, only three months, they are important as they are finding more sdBV stars than K1 did. Most importantly, K2 is discovering more p−mode pulsators with coverage not possible to get from the ground.
    Type of Medium: Online Resource
    ISSN: 2543-6376
    URL: Article
    DOI: 10.1515/astro-2018-0015
    Language: Unknown
    Publisher: Walter de Gruyter GmbH
    Publication Date: 2018
    detail.hit.zdb_id: 2908865-3
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  • 2
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    Asteroseismic analysis of variable hot subdwarf stars observed with TESS : I. The mean g -mode period spacings in hot subdwarf B stars
    EDP Sciences ; 2021
    In:  Astronomy & Astrophysics Vol. 651 ( 2021-07), p. A121-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 651 ( 2021-07), p. A121-
    Abstract: Context. We present photometric and spectroscopic analyses of gravity ( g -mode) long-period pulsating hot subdwarf B (sdB) stars, also called V1093 Her stars, observed by the TESS space telescope in both 120 s short-cadence and 20 s ultra-short-cadence mode during the survey observation and the extended mission of the southern ecliptic hemisphere. Aims. We performed a detailed asteroseismic and spectroscopic analysis of five pulsating sdB stars observed with TESS in order to compare the observations with model predictions based on our stellar evolution computations coupled with adiabatic pulsation computations. Methods. We processed and analyzed TESS observations of long-period pulsating hot subdwarf B stars. We used standard pre-whitening techniques on the datasets to extract the pulsation periods from the TESS light curves. We applied standard seismic tools for mode identification, including asymptotic period spacings and rotational frequency multiplets. Based on the values obtained from Kolmogorov-Smirnov and Inverse Variance tests, we searched for a constant period spacing for dipole ( l  = 1) and quadrupole ( l  = 2) modes. We calculated the mean period spacing for l  = 1 and l  = 2 modes and estimated the errors by means of a statistical resampling analysis. For all stars, atmospheric parameters were derived by fitting synthetic spectra to the newly obtained low-resolution spectra. We computed stellar evolution models using the LPCODE stellar evolution code, and computed l  = 1 g -mode frequencies with the adiabatic nonradial pulsation code LP-PUL . Derived observational mean period spacings were then compared to the mean period spacings from detailed stellar evolution computations coupled with the adiabatic pulsation computations of g -modes. Results. We detect 73 frequencies, most of which are identified as dipole and quadrupole g -modes with periods spanning from ∼3000 s to ∼14 500 s. The derived mean period spacing of dipole modes is concentrated in a narrow region ranging from 251 s to 256 s, while the mean period spacing for quadrupole modes spans from 145 s to 154 s. The atmospheric parameters derived from spectroscopic data are typical of long-period pulsating sdB stars with an effective temperature ranging from 23 700 K to 27 600 K and surface gravity spanning from 5.3 dex to 5.5 dex. In agreement with the expectations from theoretical arguments and previous asteroseismological works, we find that the mean period spacings obtained for models with small convective cores, as predicted by a pure Schwarzschild criterion, are incompatible with the observations. We find that models with a standard, modest convective boundary mixing at the boundary of the convective core are in better agreement with the observed mean period spacings and are therefore more realistic. Conclusions. Using high-quality space-based photometry collected by the TESS mission coupled with low-resolution spectroscopy from the ground, we provide a global comparison of the observations with model predictions by means of a robust indicator such as the mean period spacing. All five objects that we analyze in this work show remarkable homogeneity in both seismic and spectroscopic properties.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202140961
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2021
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 3
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    Meet the family − the catalog of known hot subdwarf stars
    Walter de Gruyter GmbH ; 2017
    In:  Open Astronomy Vol. 26, No. 1 ( 2017-12-20)
    Details
    In: Open Astronomy, Walter de Gruyter GmbH, Vol. 26, No. 1 ( 2017-12-20)
    Abstract: In preparation for the upcoming all-sky data releases of the Gaia mission, we compiled a catalog of known hot subdwarf stars and candidates drawn from the literature and yet unpublished databases. The catalog contains 5613 unique sources and provides multi-band photometry from the ultraviolet to the far infrared, ground based proper motions, classifications based on spectroscopy and colors, published atmospheric parameters, radial velocities and light curve variability information. Using several different techniques, we removed outliers and misclassified objects. By matching this catalog with astrometric and photometric data from the Gaia mission, we will develop selection criteria to construct a homogeneous, magnitude-limited all-sky catalog of hot subdwarf stars based on Gaia data. As first application of the catalog data, we present the quantitative spectral analysis of 280 sdB and sdOB stars from the Sloan Digital Sky Survey Data Release 7. Combining our derived parameters with state-of-the-art proper motions, we performed a full kinematic analysis of our sample. This allowed us to separate the first significantly large sample of 78 sdBs and sdOBs belonging to the Galactic halo. Comparing the properties of hot subdwarfs from the disk and the halo with hot subdwarf samples from the globular clusters ω Cen and NGC 2808, we found the fraction of intermediate He-sdOBs in the field halo population to be significantly smaller than in the globular clusters.
    Type of Medium: Online Resource
    ISSN: 2543-6376
    URL: Article
    DOI: 10.1515/astro-2017-0031
    Language: Unknown
    Publisher: Walter de Gruyter GmbH
    Publication Date: 2017
    detail.hit.zdb_id: 2908865-3
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  • 4
    Online Resource
    Online Resource
    Meet the family − the catalog of known hot subdwarf stars
    Walter de Gruyter GmbH ; 2017
    In:  Open Astronomy Vol. 26, No. 1 ( 2017-12-20), p. 164-168
    Details
    In: Open Astronomy, Walter de Gruyter GmbH, Vol. 26, No. 1 ( 2017-12-20), p. 164-168
    Abstract: In preparation for the upcoming all-sky data releases of the Gaia mission, we compiled a catalog of known hot subdwarf stars and candidates drawn from the literature and yet unpublished databases. The catalog contains 5613 unique sources and provides multi-band photometry from the ultraviolet to the far infrared, ground based proper motions, classifications based on spectroscopy and colors, published atmospheric parameters, radial velocities and light curve variability information. Using several different techniques, we removed outliers and misclassified objects. By matching this catalog with astrometric and photometric data from the Gaia mission, we will develop selection criteria to construct a homogeneous, magnitude-limited all-sky catalog of hot subdwarf stars based on Gaia data. As first application of the catalog data, we present the quantitative spectral analysis of 280 sdB and sdOB stars from the Sloan Digital Sky Survey Data Release 7. Combining our derived parameters with state-of-the-art proper motions, we performed a full kinematic analysis of our sample. This allowed us to separate the first significantly large sample of 78 sdBs and sdOBs belonging to the Galactic halo. Comparing the properties of hot subdwarfs from the disk and the halo with hot subdwarf samples from the globular clusters ! Cen and NGC 2808, we found the fraction of intermediate He-sdOBs in the field halo population to be significantly smaller than in the globular clusters.
    Type of Medium: Online Resource
    ISSN: 2543-6376
    URL: Article
    DOI: 10.1515/astro-2017-0432
    Language: English
    Publisher: Walter de Gruyter GmbH
    Publication Date: 2017
    detail.hit.zdb_id: 2908865-3
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  • 5
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    Online Resource
    Three new pulsating sdB stars discovered with SuperWASP
    Oxford University Press (OUP) ; 2017
    In:  Monthly Notices of the Royal Astronomical Society
    Details
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP)
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    URL: Article
    DOI: 10.1093/mnras/stx077
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2017
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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  • 6
    Online Resource
    Online Resource
    Radial velocity and line-profile variations in the sdBV star PG 1325+101
    Springer Science and Business Media LLC ; 2004
    In:  Astrophysics and Space Science Vol. 291, No. 3 ( 2004), p. 449-456
    Details
    In: Astrophysics and Space Science, Springer Science and Business Media LLC, Vol. 291, No. 3 ( 2004), p. 449-456
    Type of Medium: Online Resource
    ISSN: 0004-640X
    URL: Article
    DOI: 10.1023/B:ASTR.0000044359.79462.31
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2004
    detail.hit.zdb_id: 1472548-4
    detail.hit.zdb_id: 2207653-0
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  • 7
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    Detection of stellar oscillations in HWVir
    Walter de Gruyter GmbH ; 2016
    In:  Open Astronomy Vol. 26, No. 1 ( 2016-8-1), p. 199-201
    Details
    In: Open Astronomy, Walter de Gruyter GmbH, Vol. 26, No. 1 ( 2016-8-1), p. 199-201
    Abstract: We present our analysis of K2 observations of the binary system, HWVir. We processed the raw Kepler data and used Fourier analysis to search for periodic signals that could be associated with pulsations. We detect the binary frequency and its harmonic and discovered tens of peaks at both low and high frequencies. We interpreted those to be caused by stellar pulsations. Our discovery means we can apply the tools of asteroseismology to the HWVir system.
    Type of Medium: Online Resource
    ISSN: 2543-6376
    URL: Article
    DOI: 10.1515/astro-2017-0437
    Language: English
    Publisher: Walter de Gruyter GmbH
    Publication Date: 2016
    detail.hit.zdb_id: 2908865-3
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  • 8
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    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
    Oxford University Press (OUP) ; 2022
    In:  Monthly Notices of the Royal Astronomical Society Vol. 511, No. 2 ( 2022-02-11), p. 2201-2217
    Details
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 511, No. 2 ( 2022-02-11), p. 2201-2217
    Abstract: TIC 137608661/TYC 4544-2658-1/FBS 0938+788 is a new sdBV+dM reflection-effect binary discovered by the TESS space mission with an orbital period of 7.21 h. In addition to the orbital frequency and its harmonics, the Fourier transform of TIC 137608661 shows many g-mode pulsation frequencies from the subdwarf B (sdB) star. The amplitude spectrum is particularly simple to interpret as we immediately see several rotational triplets of equally spaced frequencies. The central frequencies of these triplets are equally spaced in period with a mean period spacing of 270.12 s, corresponding to consecutive l = 1 modes. From the mean frequency spacing of 1.25 μHz we derive a rotation period of 4.6 d in the deep layers of the sdB star, significantly longer than the orbital period. Among the handful of sdB+dM binaries for which the sdB rotation was measured through asteroseismology, TIC 137608661 is the non-synchronized system with both the shortest orbital period and the shortest core rotation period. Only NY Vir has a shorter orbital period but it is synchronized. From a spectroscopic follow-up of TIC 137608661 we measure the radial velocities of the sdB star, determine its atmospheric parameters, and estimate the rotation rate at the surface of the star. This measurement allows us to exclude synchronized rotation also in the outer layers and suggests a differential rotation, with the surface rotating faster than the core, as found in few other similar systems. Furthermore, an analysis of the spectral energy distribution of TIC 137608661, together with a comparison between sdB pulsation properties and asteroseismic models, gives us further elements to constrain the system.
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    URL: Article
    DOI: 10.1093/mnras/stac160
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2022
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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  • 9
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    Online Resource
    Long-term periodic variability in UV absorption lines of the Be star γ Cas: on the relation with V/R variations in the Hβ line
    Cambridge University Press (CUP) ; 1994
    In:  Symposium - International Astronomical Union Vol. 162 ( 1994), p. 376-377
    Details
    In: Symposium - International Astronomical Union, Cambridge University Press (CUP), Vol. 162 ( 1994), p. 376-377
    Abstract: We present a quantitative study of the variability in ultraviolet resonance lines of Nv, Siiv and Civ of the Be star γ Cas, following up on the work of Henrichs et al. (1983). For this purpose we used 133 IUE spectra obtained over a period of eleven years. Variability occurs in the form of discrete absorption components (DACs), which are formed in the fast-outflowing radiatively driven part of the stellar wind. We constructed a template spectrum from spectra containing no or minor extra absorption due to DACs and modelled the isolated DACs in the obtained quotient spectra. Besides the frequently observed narrow components ( v t typically ≤ 250 km/s) at high velocity, we found several broad components occurring at low and intermediate wind velocities. We confirm the finding of Doazan et al. (1987) who reported that the number of observed DACs is associated with the cyclic V/R variability of the Balmer-emission lines. This V/R variability most probably originates in the slowly outflowing high-density equatorial disc-like wind of the star (see e.g. Telting et al. 1993 for the case of γ Cas). We show that when V/R≪1 the central optical depth of DACs is significantly lower than when V/R≪1. In our interpretation this is due to a correlation between the column density associated with the DACs and the phase of the V/R cycle. We find that the Hβ observations of Doazan et al. are consistent with a model in which the cyclic V/R variability is due to a global, one-armed oscillation moving through an equatorial disc (Okazaki 1991, Papaloizou et al. 1992, Savonije and Heemskerk 1993). We suggest that the higher column density of DACs in phases of V/R≪1 is the result of the higher density in the region of their origin, namely close to or in the part of the equatorial disc which is rotating towards the observer.
    Type of Medium: Online Resource
    ISSN: 0074-1809
    URL: Article
    DOI: 10.1017/S0074180900215398
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 1994
    SSG: 16,12
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  • 10
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    Online Resource
    35th Annual Meeting of the European Association for the Study of Diabetes : Brussels, Belgium, 28 September–2 October 1999
    Springer Science and Business Media LLC ; 1999
    In:  Diabetologia Vol. 42, No. S1 ( 1999-8), p. A1-A330
    Details
    In: Diabetologia, Springer Science and Business Media LLC, Vol. 42, No. S1 ( 1999-8), p. A1-A330
    Type of Medium: Online Resource
    ISSN: 0012-186X , 1432-0428
    URL: Article
    DOI: 10.1007/BF03375458
    RVK:
    XA 40615
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 1999
    detail.hit.zdb_id: 1458993-X
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