30 research outputs found
White Dwarf Period Tables I. Pulsators with hydrogen-dominated atmospheres
We aimed at collecting all known white dwarf pulsators with hydrogen-dominated atmospheres
and list their main photometric and atmospheric parameters together with their pulsation
periods and amplitudes observed at different epochs. For this purpose, we explored the
pulsating white dwarf related literature with the systematic use of the SIMBAD and the
NASA's Astrophysics Data System (ADS) databases. We summarized our results in four tables
listing seven ZZ Ceti stars in detached white dwarf plus main-sequence binaries, seven
extremely low-mass DA pulsators, three hot DAVs and 180 ZZ Ceti stars
The Unique Frequency Spectrum of the Blazhko RRc Star LS Her
The Blazhko effect in RR Lyrae stars is still poorly understood
theoretically. Stars with multiple Blazhko periods or in which the Blazhko
effect itself varies are particularly challenging. This study investigates the
Blazhko effect in the RRc star LS Her. Detailed VRI CCD photometry has been
performed on 63 nights during six months. LS Her is confirmed to have a Blazhko
period of 12.75+/-0.02 days. However, where normally the side frequencies of
the Blazhko triplet are expected, an equidistant group of three frequencies is
found on both sides of the main pulsation frequency. As a consequence the
period and amplitude of the Blazhko effect itself vary in a cycle of 109+/-4
days. LS Her is a unique object turning out to be very important in the
verification of the theories for the Blazhko effect.Comment: Accepted for publication in MNRA
CoRoT 102749568: mode identification in a delta Scuti star based on regular spacings
The high accuracy of space data increased the number of the periodicities
determined for pulsating variable stars, but the mode identification is still a
critical point in the non-asymptotic regime. We use regularities in frequency
spacings for identifying the pulsation modes of the recently discovered delta
Sct star ID 102749568. In addition to analysing CoRoT light curves (15252
datapoints spanning 131 days), we obtained and analysed both spectroscopic and
extended multi-colour photometric data. We applied standard tools (MUFRAN,
Period04, SigSpec, and FAMIAS) for time-series analysis. A satisfactory
light-curve fit was obtaining by means of 52 independent modes and 15
combination terms. The frequency spacing revealed distinct peaks around large
(25.55-31.43 microHz), intermediate (9.80, 7.66 microHz), and low (2.35
microHz) separations. We directly identified 9 modes, and the l and n values of
other three modes were extrapolated. The combined application of spectroscopy,
multi-colour photometry, and modelling yielded the precise physical parameters
and confirmed the observational mode identification. The large separation
constrained the log g and related quantities. The dominant mode is the radial
first overtone.Comment: 13 pages, 8 figures, accepted for publication in A&
SN 2016coi/ASASSN-16fp: An example of residual helium in a type Ic supernova?
The optical observations of Ic-4 supernova (SN) 2016coi/ASASSN-16fp, from
to days after explosion, are presented along with analysis
of its physical properties. The SN shows the broad lines associated with SNe
Ic-3/4 but with a key difference. The early spectra display a strong absorption
feature at \AA\ which is not seen in other SNe~Ic-3/4 at this
epoch. This feature has been attributed to He I in the literature. Spectral
modelling of the SN in the early photospheric phase suggests the presence of
residual He in a C/O dominated shell. However, the behaviour of the He I lines
are unusual when compared with He-rich SNe, showing relatively low velocities
and weakening rather than strengthening over time. The SN is found to rise to
peak d after core-collapse reaching a bolometric luminosity of Lp
\ergs. Spectral models, including the nebular epoch, show
that the SN ejected \msun\ of material, with \msun\ below
5000 \kms, and with a kinetic energy of erg. The
explosion synthesised \msun\ of 56Ni. There are significant
uncertainties in E(B-V)host and the distance however, which will affect Lp and
MNi. SN 2016coi exploded in a host similar to the Large Magellanic Cloud (LMC)
and away from star-forming regions. The properties of the SN and the
host-galaxy suggest that the progenitor had of \msun\
and was stripped almost entirely down to its C/O core at explosion.Comment: Accepted for publication in MNRAS. Updated to reflect the published
version, minor typographical changes onl
MOST light-curve analysis of the γ Doradus pulsator HR 8799, showing resonances and amplitude variations
Context. The central star of the HR 8799 system is a γ Doradus-type pulsator. The system harbours four planetary-mass companions detected by direct imaging, and is a good solar system analogue. The masses of the companions are not accurately known because the estimation depends greatly on the age of the system, which is also not known with sufficient accuracy. Asteroseismic studies of the star might help to better constrain the age of HR 8799. We organized an extensive photometric and multi-site spectroscopic observing campaign to study the pulsations of the central star. Aims: The aim of the present study is to investigate the pulsation properties of HR 8799 in detail via the ultra-precise 47 d nearly continuous photometry obtained with the Microvariability and Oscillations in STars (MOST) space telescope, and to find as many independent pulsation modes as possible, which is the prerequisite for an asteroseismic age determination. Methods: We carried out Fourier analysis of the wide-band photometric time series. Results: We find that resonance and sudden amplitude changes characterize the pulsation of HR 8799. The dominant frequency is always at f1 = 1.978 d-1.Many multiples of one-ninth of the dominant frequency appear in the Fourier spectrum of the MOST data: n/9 f1, where n = {1,2,3,4,5,6,7,8,9,10,13,14,17,18}. Our analysis also reveals that many of these peaks show strong amplitude decrease and phase variations even on the 47 d time scale. The dependencies between the pulsation frequencies of HR 8799 make the planned subsequent asteroseismic analysis rather difficult. We point out some resemblance between the light curve of HR 8799 and the modulated pulsation light curves of Blazhko RR Lyrae stars. Based on data from the MOST satellite, a Canadian Space Agency mission, jointly operated by Dynacon Inc., the University of Toronto Institute for Aerospace Studies and the University of British Columbia, with the assistance of the University of Vienna
The Kinematic Properties of BHB and RR Lyrae stars towards the Anticentre and the North Galactic Pole: The Transition between the Inner and the Outer Halo
We identify 51 blue horizontal branch (BHB) stars, 12 possible BHB stars and
58 RR Lyrae stars in Anticentre fields. Their selection does not depend on
their kinematics. Light curves and ephemerides are given for 7 previously
unknown RR Lyrae stars. All but 4 of the RR Lyrae stars are of Oosterhoff type
I. Our selection criteria for BHB stars give results that agree with those used
by Smith et al. (2010) and Ruhland et al. (2011). We use 5 methods to determine
distances for the BHB stars and 3 methods for the RR Lyrae stars to get
distances on a uniform scale. Absolute proper motions (largely derived from the
GSCII and SDSS (DR7) databases) are given for these stars; radial velocities
are given for 31 of the BHB stars and 37 of the RR Lyrae stars. Combining these
data for BHB and RR Lyrae stars with those previously found in fields at the
North Galactic Pole, we find that retrograde orbits dominate for galactocentric
distances greater than 12.5 kpc. The majority of metal-poor stars in the solar
neighbourhood are known to be concentrated in a Lperp vs. Lz angular momentum
plot. We show that the ratio of the number of outliers to the number in the
main concentration increases with galactocentric distance. The location of
these outliers with Lperp and Lz shows that the halo BHB and RR Lyrae stars
have more retrograde orbits and a more spherical distribution with increasing
galactocentric distance. Six RR Lyrae stars are identified in the H99 group of
outliers; the small spread in their [Fe/H] suggests that they could have come
from a single globular cluster. Another group of outliers contains two pairs of
RR Lyrae stars; the stars in each pair have similar properties.Comment: 40 pages, 19 figures, to be published in MNRA
An UXor among FUors: Extinction-related Brightness Variations of the Young Eruptive Star V582 Aur
V582 Aur is an FU Ori-type young eruptive star in outburst since similar to 1985. The eruption is currently in a relatively constant plateau phase, with photometric and spectroscopic variability superimposed. Here we will characterize the progenitor of the outbursting object, explore its environment, and analyze the temporal evolution of the eruption. We are particularly interested in the physical origin of the two deep photometric dips, one that occurred in 2012 and one that is ongoing since 2016. We collected archival photographic plates and carried out new optical, infrared, and millimeter-wave photometric and spectroscopic observations between 2010 and 2018, with a high sampling rate during the current minimum. Besides analyzing the color changes during fading, we compiled multiepoch spectral energy distributions and fitted them with a simple accretion disk model. Based on pre-outburst data and a millimeter continuum measurement, we suggest that the progenitor of the V582 Aur outburst is a low-mass T Tauri star with average properties. The mass of an unresolved circumstellar structure, probably a disk, is 0.04M(circle dot). The optical and near-infrared spectra demonstrate the presence of hydrogen and metallic lines, show the CO band head in absorption, and exhibit a variable Ha profile. The color variations strongly indicate that both the similar to 1 yr long brightness dip in 2012 and the current minimum since 2016 are caused by increased extinction along the line of sight. According to our accretion disk models, the reddening changed from A(V) = 4.5 to 12.5mag, while the accretion rate remained practically constant. Similarly to the models of the UXor phenomenon of intermediate- and low-mass young stars, orbiting disk structures could be responsible for the eclipses
MOST light-curve analysis of the [gamma] Doradus pulsator HR8799, showing resonances and amplitude variations
Publisher's Version/PDFContext. The central star of the HR 8799 system is a γ Doradus-type pulsator. The system harbours four planetary-mass companions detected by direct imaging, and is a good solar system analogue. The masses of the companions are not accurately known because the estimation depends greatly on the age of the system, which is also not known with sufficient accuracy. Asteroseismic studies of the star might help to better constrain the age of HR 8799. We organized an extensive photometric and multi-site spectroscopic observing campaign to study the pulsations of the central star. Aims. The aim of the present study is to investigate the pulsation properties of HR 8799 in detail via the ultra-precise 47 d nearly continuous photometry obtained with the Microvariability and Oscillations in STars (MOST) space telescope, and to find as many independent pulsation modes as possible, which is the prerequisite for an asteroseismic age determination. Methods. We carried out Fourier analysis of the wide-band photometric time series. Results. We find that resonance and sudden amplitude changes characterize the pulsation of HR 8799. The dominant frequency is always at f1 = 1.978 d−1. Many multiples of one-ninth of the dominant frequency appear in the Fourier spectrum of the MOST data: n/9 f1, where n = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14, 17, 18}. Our analysis also reveals that many of these peaks show strong amplitude decrease and phase variations even on the 47 d time scale. The dependencies between the pulsation frequencies of HR 8799 make the planned subsequent asteroseismic analysis rather difficult. We point out some resemblance between the light curve of HR 8799 and the modulated pulsation light curves of Blazhko RR Lyrae star