281 research outputs found
The potential of space observations for pulsating pre-main sequence stars
The first asteroseismic studies of pre-main sequence (pre-MS) pulsators have
been conducted based on data from the space telescopes MOST and CoRoT with
typical time bases of less than 40 days. With these data, a relation between
the pulsational properties of pre-MS delta Scuti stars and their relative
evolutionary phase on their way from the birthline to the zero-age main
sequence was revealed. But it is evident from comparison with the more evolved
pulsators in their main sequence or post-main sequence stages observed by the
main Kepler mission, that many more questions could be addressed with
significantly longer time bases and ultra-high precision. Here, I will discuss
the observational status of pre-MS asteroseismology and the potential of future
space observations for this research field.Comment: 4 pages, 2 figures, proceedings of the conference "Seismology of the
Sun and the Distant Stars 2016", Joint TASC2 & KASC9 Workshop - SPACEINN &
HELAS8 Conferenc
Tracing early stellar evolution with asteroseismology: pre-main sequence stars in NGC 2264
Asteroseismology has been proven to be a successful tool to unravel details
of the internal structure for different types of stars in various stages of
their main sequence and post-main sequence evolution. Recently, we found a
relation between the detected pulsation properties in a sample of 34 pre-main
sequence (pre-MS) delta Scuti stars and the relative phase in their pre-MS
evolution. With this we are able to demonstrate that asteroseismology is
similarly powerful if applied to stars in the earliest stages of evolution
before the onset of hydrogen core burning.Comment: CoRoT Symposium 3 / Kepler KASC-7 joint meeting, Toulouse, July 2014.
To be published by EPJ Web of Conference
A probable pre-main sequence chemically peculiar star in the open cluster Stock 16
We used the Ultraviolet and Visual Echelle Spectrograph of the ESO-Very Large
Telescope to obtain a high resolution and high signal-to-noise ratio spectrum
of Stock 16-12, an early-type star which previous Delta-a photometric
observations suggest being a chemically peculiar (CP) star. We used spectral
synthesis to perform a detailed abundance analysis obtaining an effective
temperature of 8400 +/- 400 K, a surface gravity of 4.1 +/- 0.4, a
microturbulence velocity of 3.4 +0.7/-0.3 km/s, and a projected rotational
velocity of 68 +/- 4 km/s. We provide photometric and spectroscopic evidence
showing the star is most likely a member of the young Stock 16 open cluster
(age 3-8 Myr). The probable cluster membership, the star's position in the
Hertzsprung-Russell diagram, and the found infrared excess strongly suggest the
star is still in the pre-main-sequence (PMS) phase. We used PMS evolutionary
tracks to determine the stellar mass, which ranges between 1.95 and 2.3 Msun,
depending upon the adopted spectroscopic or photometric data results.
Similarly, we obtained a stellar age ranging between 4 and 6 Myr, in agreement
with that of the cluster. Because the star's chemical abundance pattern
resembles well that known of main sequence CP metallic line (Am) stars, the
object sets important constraints to the diffusion theory. Additional
spectroscopic and spectropolarimetric data allowed us to conclude that the
object is probably a single non-magnetic star.Comment: Accepted for publication in MNRAS; 8 pages, 5 figures, 1 tabl
The imprint of star formation on stellar pulsations
In the earliest phases of their evolution, stars gain mass through the
acquisition of matter from their birth clouds. The widely accepted classical
concept of early stellar evolution neglects the details of this accretion phase
and assumes the formation of stars with large initial radii that contract
gravitationally. In this picture, the common idea is that once the stars begin
their fusion processes, they have forgotten their past. By analysing stellar
oscillations in recently born stars, we show that the accretion history leaves
a potentially detectable imprint on the stars' interior structures. Currently
available data from space would allow discriminating between these more
realistic accretion scenarios and the classical early stellar evolution models.
This opens a window to investigate the interior structures of young pulsating
stars that will also be of relevance for related fields, such as stellar
oscillations in general and exoplanet studies.Comment: Open Access published in Nature Communications Supplementary Material
is available at https://www.nature.com/articles/s41467-022-32882-
Pre-main sequence variable stars in young open cluster NGC 1893
We present results of multi-epoch (fourteen nights during 2007-2010) -band
photometry of the cluster NGC 1893 region to identify photometric variable
stars in the cluster. The study identified a total of 53 stars showing
photometric variability. The members associated with the region are identified
on the basis of spectral energy distribution, two colour diagram and
colour-magnitude diagram. The ages and masses of the majority of
pre-main-sequence sources are found to be 5 Myr and in the range 0.5
4, respectively. These pre-main-sequence
sources hence could be T Tauri stars. We also determined the physical
parameters like disk mass and accretion rate from the spectral energy
distribution of these T Tauri stars. The periods of majority of the T Tauri
stars range from 0.1 to 20 day. The brightness of Classical T Tauri stars is
found to vary with larger amplitude in comparison to Weak line T Tauri stars.
It is found that the amplitude decreases with increase in mass, which could be
due to the dispersal of disks of massive stars.Comment: 15pages, 16 figures and 5 tables, Accepted for publication in MNRA
gamma Doradus pulsation in two pre-main sequence stars discovered by CoRoT
Pulsations in pre-main sequence stars have been discovered several times
within the last years. But nearly all of these pulsators are of delta
Scuti-type. gamma Doradus-type pulsation in young stars has been predicted by
theory, but lack observational evidence. We present the investigation of
variability caused by rotation and (gammaDoradus-type) pulsation in two
pre-main sequence members of the young open cluster NGC2264 using
high-precision time series photometry from the CoRoT satellite and dedicated
high-resolution spectroscopy. Time series photometry of NGC2264VAS20 and NGC
2264VAS87 was obtained by the CoRoT satellite during the dedicated short run
SRa01 in March 2008. NGC2264VAS87 was re-observed by CoRoT during the short run
SRa05 in December 2011 and January 2012. Frequency analysis was conducted using
Period04 and SigSpec. The spectral analysis was performed using equivalent
widths and spectral synthesis. The frequency analysis yielded 10 and 14
intrinsic frequencies for NGC2264VAS20 and NGC2264VAS 87, respectively, in the
range from 0 to 1.5c/d which are attributed to be caused by a combination of
rotation and pulsation. The effective temperatures were derived to be
6380150K for NGC2264VAS20 and 6220150K for NGC2264VAS87. Membership
of the two stars to the cluster is confirmed independently using X-ray fluxes,
radial velocity measurements and proper motions available in the literature.
The derived Li abundances of log n(Li)=3.34 and 3.54 for NGC2264VAS20 and
NGC2264VAS87, respectively, are in agreement with the Li abundance for other
stars in NGC2264 of similar Teff reported in the literature. We conclude that
the two objects are members of NGC2264 and therefore are in their pre-main
sequence evolutionary stage. Assuming that part of their variability is caused
by pulsation, these two stars might be the first pre-main sequence gamma
Doradus candidates.Comment: 11 pages, 10 figures, A&A accepte
Investigating star formation in the young open cluster NGC 6383
By studying young open clusters, the mechanisms important for star formation
over several Myr can be examined. For example, accretion rate as a function of
rotational velocity can be investigated. Similarly, sequential star formation
triggered by massive stars with high mass-loss rates can be studied in detail.
We identified and characterized probable members of NGC 6383, as well as
determined cluster parameters. New Stromgren uvby CCD photometry, obtained by
us, is presented. This new data, together with Johnson UBV and 2MASS data in
the NIR, was used to investigate characteristics of pre- as well as zero age
main sequence cluster members. We present Stromgren uvby CCD photometry for 272
stars in the field of NGC 6383 and derive its reddening, E(b-y)=0.21(4)mag, as
well as distance, d=1.7(3)kpc from the Sun. Several stars with NIR excess and
objects in the domain of the classical Herbig Ae/Be and T Tauri stars were
detected. Two previously known variables were identified as rapidly-rotating
PMS stars. The field population is clearly separated from the probable members
in the color-magnitude diagram. NGC 6383 is a young open cluster, with an age
of less than 4 Myr, undergoing continuous star formation. True pre-main
sequence members might be found down to absolute magnitudes of +6mag, with a
variety of rotational velocities and stellar activities.Comment: 7 pages, 6 figures, accepted by A&
The complex fossil magnetic field of the Scuti star HD\,41641
Only three magnetic Scuti stars are known as of today. HD 41641 is a
Scuti star showing chemical peculiarities and rotational modulation of
its light-curve, making it a good magnetic candidate. We acquired
spectropolarimetric observations of this star with Narval at TBL to search for
the presence of a magnetic field and characterize it. We indeed clearly detect
a magnetic field in HD 41641, making it the fourth known magnetic
Scuti star. Our analysis shows that the field is of fossil origin, like
magnetic OBA stars, but with a complex field structure rather than the much
more usual dipolar structure.Comment: 9 pages, 6 figures, 5 tables plus 1 in appendi
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