2,784 research outputs found
The IACOB project: I. Rotational velocities in Northern Galactic O and early B-type stars revisited. The impact of other sources of line-broadening
Stellar rotation is an important parameter in the evolution of massive stars.
Accurate and reliable measurements of projected rotational velocities in large
samples of OB stars are crucial to confront the predictions of stellar
evolutionary models with observational constraints. We reassess previous
determinations of projected rotational velocities (vsini) in Galactic OB stars
using a large, high quality spectroscopic dataset, and a strategy which account
for other sources of broadening appart from rotation affecting the diagnostic
lines We present a versatile and user friendly IDL tool, based on a combined
Fourier Transform (FT) + goodness of fit (GOF) methodology, for the
line-broadening characterization in OB-type stars. We use this tool to (a)
investigate the impact of macroturbulent and microturbulent broadenings on
vsini measurements, and (b) determine vsini in a sample of 200 Galactic OB-type
stars, also characterizing the amount of macroturbulent broadening (\vmacro)
affecting the line profiles. We present observational evidence illustrating the
strengths and limitations of the proposed FT+GOF methodology for the case of OB
stars. We confirm previous statements (based on indirect arguments or smaller
samples) that the macroturbulent broadening is ubiquitous in the massive star
domain. We compare the newly derived vsini with previous determinations not
accounting for this extra line-broadening contribution, and show that those
cases with vsini< 120 km/s need to be systematically revised downwards by ~25
(+/-20) km/s. We suggest that microturbulence may impose an upper limit below
which vsini and \vmacro\ could be incorrectly derived by means of the proposed
methodology as presently used, and discuss the implications of this statement
on the study of relatively narrow line massive stars.Comment: Accepted for publication in A&A (19 pages, 15 figures, 6 tables).
Tables A1-A5 will be make available in the final edited version of the paper
(or under request to SS-D
The IACOB project: A grid-based automatic tool for the quantitative spectroscopic analysis of O-stars
We present the IACOB grid-based automatic tool for the quantitative
spectroscopic analysis of O-stars. The tool consists of an extensive grid of
FASTWIND models, and a variety of programs implemented in IDL to handle the
observations, perform the automatic analysis, and visualize the results. The
tool provides a fast and objective way to determine the stellar parameters and
the associated uncertainties of large samples of O-type stars within a
reasonable computational time.Comment: 8 pages, 2 figures, 1 table. Proceedings of the "GREAT-ESF Stellar
Atmospheres in the Gaia Era Workshop
OB stars at the lowest Local Group metallicity: GTC-OSIRIS observations of Sextans A
Our aim is to find and classify OB stars in Sextans A, to later determine
accurate stellar parameters of these blue massive stars in this low metallicity
region .
Using UBV photometry, the reddening-free index Q and GALEX imaging, we built
a list of blue massive star candidates in Sextans A. We obtained low resolution
(R 1000) GTC-OSIRIS spectra for a fraction of them and carried out
spectral classification. For the confirmed O-stars we derive preliminary
stellar parameters.
The target selection criteria and observations were successful and have
produced the first spectroscopic atlas of OB-type stars in Sextans A. From the
whole sample of 18 observed stars, 12 were classified as early OB-types,
including 5 O-stars. The radial velocities of all target stars are in agreement
with their Sextans A membership, although three of them show significant
deviations. We determined the stellar parameters of the O-type stars using the
stellar atmosphere code FASTWIND, and revisited the sub-SMC temperature scale.
Two of the O-stars are consistent with relatively strong winds and enhanced
helium abundances, although results are not conclusive. We discuss the position
of the OB stars in the HRD. Initial stellar masses run from slightly below 20
up to 40 solar masses.
The target selection method worked well for Sextans A, confirming the
procedure developed in Garcia \& Herrero (2013). The stellar temperatures are
consistent with findings in other galaxies. Some of the targets deserve
follow-up spectroscopy because of indications of a runaway nature, an enhanced
helium abundance or a relatively strong wind. We observe a correlation between
HI and OB associations similar to the irregular galaxy IC1613, confirming the
previous result that the most recent star formation of Sextans A is currently
on-going near the rim of the H\,{\sc I} cavity
The little-studied cluster Berkeley 90. II. The foreground ISM
Context: Nearly one century after their discovery, the carrier(s) of Diffuse
Interstellar Bands is/are still unknown and there are few sightlines studied in
detail for a large number of DIBs. Aims: We want to study the ISM sightlines
towards LS III +46 11 and LS III +46 12, two early-O-type stellar systems, and
LS III +46 11 B, a mid-B-type star. The three targets are located in the
stellar cluster Berkeley 90 and have a high extinction. Methods: We use the
multi-epoch high-S/N optical spectra presented in paper I (Ma\'iz Apell\'aniz
et al. 2015), the extinction results derived there, and additional spectra.
Results: We have measured equivalent widths, velocities, and FWHMs for a large
number of absorption lines in the rich ISM spectrum in front of Berkeley 90.
The absorbing ISM has at least two clouds at different velocities, one with a
lower column density (thinner) in the K I lines located away from Berkeley 90
and another one with a higher column density (thicker) associated with the
cluster. The first cloud has similar properties for both O-star sightlines but
the second one is thicker for LS III +46 11. The comparison between species
indicate that the cloud with a higher column density has a denser core,
allowing us to classify the DIBs in a sigma-zeta scale, some of them for the
first time. The LS III +46 12 sightline also has a high-velocity redshifted
component.Comment: Accepted for publication in A&
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