123,333 research outputs found
A Mid-Infrared Imaging Survey of Embedded Young Stellar Objects in the Rho Ophiuchi Cloud Core
Results of a comprehensive, new, ground-based mid-infrared imaging survey of
the young stellar population of the Rho Ophiuchi cloud are presented. Data were
acquired at the Palomar 5-m and at the Keck 10-m telescopes with the MIRLIN and
LWS instruments, at 0.25 arcsec and 0.25 arcsec resolutions, respectively. Of
172 survey objects, 85 were detected. Among the 22 multiple systems observed,
15 were resolved and their individual component fluxes determined. A plot of
the frequency distribution of the detected objects with SED spectral slope
shows that YSOs spend ~400,000 yr in the Flat Spectrum phase, clearing out
their remnant infall envelopes. Mid-infrared variability is found among a
significant fraction of the surveyed objects, and is found to occur for all SED
classes with optically thick disks. Large-amplitude near-infrared variability,
also found for all SED classes with optically thick disks, seems to occur with
somewhat higher frequency at the earlier evolutionary stages. Although a
general trend of mid-infrared excess and NIR veiling exists proceeding through
SED classes, with Class I objects generally exhibiting K-veilings > 1, Flat
Spectrum objects with K-veilings > 0.58, and Class III objects with K-veilings
=0, Class II objects exhibit the widest range of K-band veiling values, 0-4.5.
However, the highly variable value of veiling that a single source can exhibit
in any of the SED classes in which active disk accretion can take place is
striking, and is direct observational evidence for highly time-variable
accretion activity in disks. Finally, by comparing mid-infrared vs.
near-infrared excesses in a subsample with well-determined effective
temperatures and extinction values, disk clearing mechanisms are explored. The
results are consistent with disk clearing proceeding from the inside-out.Comment: 18 pages + 5 tables + 7 figure
Asteroseismology of massive stars with the TESS mission: the runaway Beta Cep pulsator PHL 346 = HN Aqr
We report an analysis of the first known Beta Cep pulsator observed by the
TESS mission, the runaway star PHL 346 = HN Aqr. The star, previously known as
a singly-periodic pulsator, has at least 34 oscillation modes excited, 12 of
those in the g-mode domain and 22 p modes. Analysis of archival data implies
that the amplitude and frequency of the dominant mode and the stellar radial
velocity were variable over time. A binary nature would be inconsistent with
the inferred ejection velocity from the Galactic disc of 420 km/s, which is too
large to be survivable by a runaway binary system. A kinematic analysis of the
star results in an age constraint (23 +- 1 Myr) that can be imposed on
asteroseismic modelling and that can be used to remove degeneracies in the
modelling process. Our attempts to match the excitation of the observed
frequency spectrum resulted in pulsation models that were too young. Hence,
asteroseismic studies of runaway pulsators can become vital not only in tracing
the evolutionary history of such objects, but to understand the interior
structure of massive stars in general. TESS is now opening up these stars for
detailed asteroseismic investigation.Comment: accepted for ApJ
Multi-site observations of Delta Scuti stars 7 Aql and 8 Aql (a new Delta Scuti variable): The twelfth STEPHI campaign in 2003
We present an analysis of the pulsation behaviour of the Delta Scuti stars 7
Aql (HD 174532) and 8 Aql (HD 174589) -- a new variable star -- observed in the
framework of STEPHI XII campaign during 2003 June--July. 183 hours of high
precision photometry were acquired by using four-channel photometers at three
sites on three continents during 21 days. The light curves and amplitude
spectra were obtained following a classical scheme of multi-channel photometry.
Observations in different filters were also obtained and analyzed. Six and
three frequencies have been unambiguously detected above a 99% confidence level
in the range 0.090 mHz--0.300 mHz and 0.100 mHz-- 0.145 mHz in 7 Aql and 8 Aql
respectively. A comparison of observed and theoretical frequencies shows that 7
Aql and 8 Aql may oscillate with p modes of low radial orders, typical among
Delta Scuti stars. In terms of radial oscillations the range of 8 Aql goes from
n=1 to n=3 while for 7 Aql the range spans from n=4 to n=7. Non-radial
oscillations have to be present in both stars as well. The expected range of
excited modes according to a non adiabatic analysis goes from n=1 to n=6 in
both stars.Comment: 8 pages, 7 fugures, 5 tables, accepted for publication in
Astronomical Journa
The evolutionary status of the bright high-latitude supergiant HD190390
Despite its mean apparent magnitude of m(v)=6.39, the evolutionary status of
HD190390 (HR7671), a luminous F-type supergiant at high galactic latitude, is
still not very clear, but in most papers a post-AGB classification is assumed.
New observational material has been obtained with four different instruments
and is presented here. An extensive abundance analysis based on high
resolution, high signal-to-noise NTT+EMMI spectra confirms the metal deficiency
of this object ([Fe/H]=-1.6), together with a high lithium content
(log(Li)=1.9). A variability analysis based on Geneva photometry over seven
years reveals beating with a period of +/-3000 days. It is, however, not clear
whether this beating is caused by a stable triplet, or it is the consequence of
small changes in the main frequency. More recent data obtained with the
HIPPARCOS satellite and the Mercator telescope not only confirm the main
period, but also support the presence of a second periodicity of 11 days, which
was also found in the Geneva photometry. A conclusive evolutionary status of
this object is not given, but alternative to the UU Her (i.e. post-AGB) status,
a W Vir classification is discussed.Comment: 14 pages, 13 figures, accepted for publication in A&
Purifying Selection in Deeply Conserved Human Enhancers Is More Consistent than in Coding Sequences
(c) 2014 De Silva et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Asteroseismological studies of three Beta Cephei stars: IL Vel, V433 Car and KZ Mus
We have acquired between 127 and 150 h of time-resolved multicolour
photometry for each of the three Beta Cephei stars IL Vel, V433 Car and KZ Mus
over a time span of four months from two observatories. All three objects are
multiperiodic with at least three modes of pulsation. Mode identification from
the relative colour amplitudes is performed. We obtain unambiguous results for
the two highest-amplitude modes of IL Vel (both are l=1) and the three
strongest modes of KZ Mus (l=2,0 and 1), but none for V433 Car. Spectroscopy
shows the latter star to be a fast rotator (v sin i = 240 km/s), whereas the
other two have moderate v sin i (65 and 47 km/s, respectively). We performed
model calculations with the Warsaw-New Jersey stellar evolution and pulsation
code. We find that IL Vel is an object of about 12 Msun in the second half of
its main sequence evolutionary track. Its two dipole modes are most likely
rotationally split components of the mode originating as p1 on the ZAMS; one of
these modes is m=0. V433 Car is suggested to be an unevolved 13 Msun star just
entering the Beta Cephei instability strip. KZ Mus seems less massive (about
12.7 Msun) and somewhat more evolved, and its radial mode is probably the
fundamental one. In this case its quadrupole mode would be the one originating
as g1, and its dipole mode would be p1. It is suggested that mode
identification of slowly rotating Beta Cephei stars based on photometric colour
amplitudes is reliable; we estimate that a relative accuracy of 3% in the
amplitudes is sufficient for unambiguous identifications. Due to the good
agreement of our theoretical and observational results we conclude that the
prospects for asteroseismology of multiperiodic slowly rotating Beta Cephei
star are good.Comment: 16 pages, 16 figures, MNRAS, in pres
Period spacings in red giants II. Automated measurement
The space missions CoRoT and Kepler have provided photometric data of
unprecedented quality for asteroseismology. A very rich oscillation pattern has
been discovered for red giants, including mixed modes that are used to decipher
the red giants interiors. They carry information on the radiative core of red
giant stars and bring strong constraints on stellar evolution. Since more than
15,000 red giant light curves have been observed by Kepler, we have developed a
simple and efficient method for automatically characterizing the mixed-mode
pattern and measuring the asymptotic period spacing. With the asymptotic
expansion of the mixed modes, we have revealed the regularity of the
gravity-mode pattern. The stretched periods were used to study the evenly space
periods with a Fourier analysis and to measure the gravity period spacing, even
when rotation severely complicates the oscillation spectra. We automatically
measured gravity period spacing for more than 6,100 Kepler red giants. The
results confirm and extend previous measurements made by semi-automated
methods. We also unveil the mass and metallicity dependence of the relation
between the frequency spacings and the period spacings for stars on the red
giant branch. The delivery of thousands of period spacings combined with all
other seismic and non-seismic information provides a new basis for detailed
ensemble asteroseismology.Comment: 13 pages, 13 figure
CoRoT\,102699796, the first metal-poor Herbig Ae pulsator: a hybrid Sct- Dor variable?
We present the analysis of the time series observations of CoRoT\,102699796
obtained by the CoRoT satellite that show the presence of five independent
oscillation frequencies in the range 3.6-5 c/d. Using spectra acquired with
FLAMES@VLT, we derive the following stellar parameters: spectral type F1V,
T=7000200 K, log(g)=, [M/H]=,
sin= km/s, L/L=21. Thus, for the first
time we report the existence of a metal poor, intermediate-mass PMS pulsating
star. Ground-based and satellite data are used to derive the spectral energy
distribution of CoRoT\,102699796 extending from the optical to mid-infrared
wavelengths. The SED shows a significant IR excess at wavelengths greater than
. We conclude that CoRoT\,102699796 is a young Herbig Ae (F1Ve) star
with a transitional disk, likely associated to the HII region [FT96]213.1-2.2.
The pulsation frequencies have been interpreted in the light of the
non-radial pulsation theory, using the LOSC code in conjunction with static and
rotational evolutionary tracks. A minimization algorithm was used to find the
best-fit model with M=1.84 M, T=6900 K which imply an
isochronal age of t2.5 Myr. This result is based on the interpretation of
the detected frequencies as -modes of low-moderate -value. To our
knowledge, this is the first time that such modes are identified in a
intermediate-mass PMS pulsating star. Since CoRoT\,102699796 lies in the region
of the HR diagram where the Sct and Dor instability strips
intersect, we argue that the observed pulsation characteristics are
intermediate between these classes of variables, i.e. CoRoT\,102699796 is
likely the first PMS hybrid Dor- Sct pulsator ever studied.Comment: 13 pages, 7 figures. Accepted for publication in Monthly Notices of
the RA
Preparing the COROT space mission: new variable stars in the galactic Anticenter direction
The activities related to the preparation of the asteroseismic, photometric
space mission COROT are described. Photoelectric observations, wide--field CCD
photometry, uvbyB calibrations and further time--series have been obtained at
different observatories and telescopes. They have been planned to complete the
COROT programme in the direction of the galactic Anticenter. In addition to
suitable asteroseismic targets covering the different evolutionary stages
between ZAMS and TAMS, we discovered several other variable stars, both
pulsating and geometrical. We compared results on the incidence of variability
in the galactic Center and Anticenter directions. Physical parameters have been
obtained and evolutionary tracks fitting them have been calculated. The
peculiarities of some individual stars alre pointed out. Paper based on
observations collected at the San Pedro Martir, Sierra Nevada, Teide, La Silla,
Haute-Provence and Roque de Los Muchachos (Telescopio Nazionale Galileo and
Mercator telescopes) observatories.Comment: 13 pages, 9 figures. Accepted for The Astronomical Journal (2005 May
volume
- âŠ