46 research outputs found
The Stony Brook / SMARTS Atlas of mostly Southern Novae
We introduce the Stony Brook / SMARTS Atlas of (mostly) Southern Novae. This
atlas contains both spectra and photometry obtained since 2003. The data
archived in this atlas will facilitate systematic studies of the nova
phenomenon and correlative studies with other comprehensive data sets. It will
also enable detailed investigations of individual objects. In making the data
public we hope to engender more interest on the part of the community in the
physics of novae. The atlas is on-line at
\url{http://www.astro.sunysb.edu/fwalter/SMARTS/NovaAtlas/} .Comment: 11 figures; 5 table
TW Hydrae: evidence of stellar spots instead of a Hot Jupiter
TW Hydrae shows significant radial-velocity variations in the optical regime.
They have been attributed to a 10 Jupiter Mass planet orbiting the star at 0.04
AU. In this work, we have tested whether the observed RV variations can be
caused by stellar spots. We have also analyzed new optical and infrared data to
confirm the signal of the planet companion. We fitted the RV variations of TW
Hya using a cool spot model. Our model shows that a cold spot covering 7% of
the stellar surface and located at a latitude of 54 deg can reproduce the
reported RV variations. The model also predicts a bisector semi-amplitude
variation <10 m/s, which is less than the errors of the RV measurements
discussed in an earlier publication. The analysis of new optical RV data, with
typical errors of 10 m/s, shows a larger RV amplitude that varies depending on
the correlation mask used. A slight correlation between the RV variation and
the bisector is also observed, although not at a very significant level. The
infrared H-band RV curve is almost flat, showing a small variation (<35 m/s)
that is not consistent with the optical orbit. All these results support the
spot scenario rather than the presence of a hot Jupiter around TW Hya.Comment: accepted for publication in A&
The HgMn Binary Star Phi Herculis: Detection and Properties of the Secondary and Revision of the Elemental Abundances of the Primary
Observations of the Mercury-Manganese star Phi Herculis with the Navy
Prototype Optical Interferometer (NPOI) conclusively reveal the previously
unseen companion in this single-lined binary system. The NPOI data were used to
predict a spectral type of A8V for the secondary star Phi Her B. This
prediction was subsequently confirmed by spectroscopic observations obtained at
the Dominion Astrophysical Observatory. Phi Her B is rotating at 50 +/-3
km/sec, in contrast to the 8 km/sec lines of Phi Her A. Recognizing the lines
from the secondary permits one to separate them from those of the primary. The
abundance analysis of Phi Her A shows an abundance pattern similar to those of
other HgMn stars with Al being very underabundant and Sc, Cr, Mn, Zn, Ga, Sr,
Y, Zr, Ba, Ce, and Hg being very overabundant.Comment: Accepted to ApJ, 45 pages, 11 figure
Synthetic High-Resolution Line Spectra of Star-Forming Galaxies Below 1200A
We have generated a set of far-ultraviolet stellar libraries using spectra of
OB and Wolf-Rayet stars in the Galaxy and the Large and Small Magellanic Cloud.
The spectra were collected with the Far Ultraviolet Spectroscopic Explorer and
cover a wavelength range from 1003.1 to 1182.7A at a resolution of 0.127A. The
libraries extend from the earliest O- to late-O and early-B stars for the
Magellanic Cloud and Galactic libraries, respectively. Attention is paid to the
complex blending of stellar and interstellar lines, which can be significant,
especially in models using Galactic stars. The most severe contamination is due
to molecular hydrogen. Using a simple model for the H line strength, we
were able to remove the molecular hydrogen lines in a subset of Magellanic
Cloud stars. Variations of the photospheric and wind features of CIII 1176, OVI
1032, 1038, PV 1118, 1128, and SIV 1063, 1073, 1074 are discussed as a function
of temperature and luminosity class. The spectral libraries were implemented
into the LavalSB and Starburst99 packages and used to compute a standard set of
synthetic spectra of star-forming galaxies. Representative spectra are
presented for various initial mass functions and star formation histories. The
valid parameter space is confined to the youngest ages of less than 10 Myr for
an instantaneous burst, prior to the age when incompleteness of spectral types
in the libraries sets in. For a continuous burst at solar metallicity, the
parameter space is not limited. The suite of models is useful for interpreting
the restframe far-ultraviolet in local and high-redshift galaxies.Comment: 33 pages including 13 figures, accepted for publication in Ap
Kepler observations of variability in B-type stars
The analysis of the light curves of 48 B-type stars observed by Kepler is
presented. Among these are 15 pulsating stars, all of which show low
frequencies characteristic of SPB stars. Seven of these stars also show a few
weak, isolated high frequencies and they could be considered as SPB/beta Cep
hybrids. In all cases the frequency spectra are quite different from what is
seen from ground-based observations. We suggest that this is because most of
the low frequencies are modes of high degree which are predicted to be unstable
in models of mid-B stars. We find that there are non-pulsating stars within the
beta Cep and SPB instability strips. Apart from the pulsating stars, we can
identify stars with frequency groupings similar to what is seen in Be stars but
which are not Be stars. The origin of the groupings is not clear, but may be
related to rotation. We find periodic variations in other stars which we
attribute to proximity effects in binary systems or possibly rotational
modulation. We find no evidence for pulsating stars between the cool edge of
the SPB and the hot edge of the delta Sct instability strips. None of the stars
show the broad features which can be attributed to stochastically-excited modes
as recently proposed. Among our sample of B stars are two chemically peculiar
stars, one of which is a HgMn star showing rotational modulation in the light
curve.Comment: 19 pages, 11 figures, 4 table
No magnetic field in the spotted HgMn star mu Leporis
Chemically peculiar stars of the mercury-manganese (HgMn) type represent a
new class of spotted late-B stars, in which evolving surface chemical
inhomogeneities are apparently unrelated to the presence of strong magnetic
fields but are produced by some hitherto unknown astrophysical mechanism. The
goal of this study is to perform a detailed line profile variability analysis
and carry out a sensitive magnetic field search for one of the brightest HgMn
stars - mu Lep. We acquired a set of very high-quality intensity and
polarization spectra of mu Lep with the HARPSpol polarimeter. These data were
analyzed with the multiline technique of least-squares deconvolution in order
to extract information on the magnetic field and line profile variability. Our
spectra show very weak but definite variability in the lines of Sc, all Fe-peak
elements represented in the spectrum of mu Lep, as well as Y, Sr, and Hg.
Variability might also be present in the lines of Si and Mg. Anomalous profile
shapes of Ti II and Y II lines suggest a dominant axisymmetric distribution of
these elements. At the same time, we found no evidence of the magnetic field in
mu Lep, with the 3 sigma upper limit of only 3 G for the mean longitudinal
magnetic field. This is the most stringent upper limit on the possible magnetic
field derived for a spotted HgMn star. The very weak variability detected for
many elements in the spectrum mu Lep suggests that low-contrast chemical
inhomogeneities may be common in HgMn stars and that they have not been
recognized until now due to the limited precision of previous spectroscopic
observations and a lack of time-series data. The null result of the magnetic
field search reinforces the conclusion that formation of chemical spots in HgMn
stars is not magnetically driven.Comment: Accepted for publication in Astronomy & Astrophysic
Magnetism, chemical spots, and stratification in the HgMn star phi Phoenicis
Mercury-manganese (HgMn) stars have been considered as non-magnetic and
non-variable chemically peculiar (CP) stars for a long time. However, recent
discoveries of the variability in spectral line profiles have suggested an
inhomogeneous surface distribution of chemical elements in some HgMn stars.
From the studies of other CP stars it is known that magnetic field plays a key
role in the formation of surface spots. All attempts to find magnetic fields in
HgMn stars have yielded negative results. In this study, we investigate the
possible presence of a magnetic field in phi Phe (HD 11753) and reconstruct
surface distribution of chemical elements that show variability in spectral
lines.We also test a hypothesis that a magnetic field is concentrated in
chemical spots and look into the possibility that some chemical elements are
stratified with depth in the stellar atmosphere. Our analysis is based on
high-quality spectropolarimetric time-series observations, covering a full
rotational period of the star. Spectra were obtained with the HARPSpol at the
ESO 3.6-m telescope. Combining information from all suitable spectral lines, we
set an upper limit of 4 G on the mean longitudinal magnetic field. For chemical
spots, an upper limit on the longitudinal field varies between 8 and 15 G. We
confirmed the variability of Y, Sr, and Ti and detected variability in Cr
lines. Stratification analysis showed that Y and Ti are not concentrated in the
uppermost atmospheric layers. Our spectropolarimetric observations rule out the
presence of a strong, globally-organised magnetic field in phi Phe. This
implies an alternative mechanism of spot formation, which could be related to a
non-equilibrium atomic diffusion. However, the typical time scales of the
variation in stratification predicted by the recent time-dependent diffusion
models exceed significantly the spot evolution time-scale reported for phi Phe.Comment: Accepted for publication in Astronomy & Astrophysics, 15 pages, 15
figure
The Tarantula Massive Binary Monitoring: I. Observational campaign and OB-type spectroscopic binaries
© ESO, 2017.Context. Massive binaries play a crucial role in the Universe. Knowing the distributions of their orbital parameters is important for a wide range of topics from stellar feedback to binary evolution channels and from the distribution of supernova types to gravitational wave progenitors, yet no direct measurements exist outside the Milky Way. Aims. The Tarantula Massive Binary Monitoring project was designed to help fill this gap by obtaining multi-epoch radial velocity (RV) monitoring of 102 massive binaries in the 30 Doradus region. Methods. In this paper we analyze 32 FLAMES/GIRAFFE observations of 93 O- and 7 B-type binaries. We performed a Fourier analysis and obtained orbital solutions for 82 systems: 51 single-lined (SB1) and 31 double-lined (SB2) spectroscopic binaries. Results. Overall, the binary fraction and orbital properties across the 30 Doradus region are found to be similar to existing Galactic samples. This indicates that within these domains environmental effects are of second order in shaping the properties of massive binary systems. A small difference is found in the distribution of orbital periods, which is slightly flatter (in log space) in 30 Doradus than in the Galaxy, although this may be compatible within error estimates and differences in the fitting methodology. Also, orbital periods in 30 Doradus can be as short as 1.1 d, somewhat shorter than seen in Galactic samples. Equal mass binaries (q> 0.95) in 30 Doradus are all found outside NGC 2070, the central association that surrounds R136a, the very young and massive cluster at 30 Doradus's core. Most of the differences, albeit small, are compatible with expectations from binary evolution. One outstanding exception, however, is the fact that earlier spectral types (O2-O7) tend to have shorter orbital periods than later spectral types (O9.2-O9.7). Conclusions. Our results point to a relative universality of the incidence rate of massive binaries and their orbital properties in the metallicity range from solar (Z) to about half solar. This provides the first direct constraints on massive binary properties in massive star-forming galaxies at the Universe's peak of star formation at redshifts z ~ 1 to 2 which are estimated to have Z 0.5 Z
Eclipses by circumstellar material in the T Tauri star AA Tau. II. Evidence for non-stationary magnetospheric accretion
We report the results of a synoptic study of the photometric and
spectroscopic variability of the classical T Tauri star AA Tau on timescales
ranging from a few hours to several weeks. Emission lines show both infall and
outflow signatures and are well reproduced by magnetospheric accretion models
with moderate mass accretion rates and high inclinations. The veiling shows
variations that indicate the presence of 2 rotationally modulated hot spots
corresponding to the two magnetosphere poles. It correlates well with the HeI
line flux, with B-V and the V excess flux. We have indications of a time delay
between the main emission lines and veiling, the lines formed farther away
preceding the veiling changes. The time delay we measure is consistent with
accreted material propagating downwards the accretion columns at free fall
velocity from a distance of about 8 Rstar. We also report periodic radial
velocity variations of the photospheric spectrum which might point to the
existence of a 0.02 Msun object orbiting the star at a distance of 0.08 AU.
During a few days, the variability of the system was strongly reduced and the
line fluxes and veiling severely depressed. We argue that this episode of
quiescence corresponds to the temporary disruption of the magnetic
configuration at the disk inner edge. The radial velocity variations of inflow
and outflow diagnostics in the Halpha profile yield further evidence for large
scale variations of the magnetic configuration on a timescale of a month. These
results may provide the first clear evidence for large scale instabilities
developping in T Tauri magnetospheres as the magnetic field lines are twisted
by differential rotation between the star and the inner disk.Comment: 25 pages, Astron. Astrophys., in pres