297 research outputs found
The infrared Hourglass cluster in M8
A detailed study of the Hourglass Nebula in the M8 star forming region is
presented. The study is mainly based on recent subarcsec-resolution JHKs images
taken at Las Campanas Observatory and complemented with archival HST images and
longslit spectroscopy retrieved from the ESO Archive Facility. Using the new
numerical code CHORIZOS, we estimate the distance to the earliest stars in the
region to be 1.25 kpc. Infrared photometry of all the sources detected in the
field is given. From analysis of the JHKs colour-colour diagrams, we find that
an important fraction of these sources exhibit significant infrared excess.
These objects are candidates to be low- and intermediate-mass pre-main sequence
stars. Based on HST observations, the spatial distribution of gas, dust and
stars in the region is analyzed. The morphological analysis of these images
also reveals a rich variety of structures related to star formation (proplyds,
jets, bow shocks), similar to those observed in M16 and M42, along with the
detection of the first four Herbig-Haro objects in the region. Furthermore, a
longslit spectrum obtained with NTT confirms the identification of one of them
(HH 870) in the core of the Hourglass nebula, providing the first direct
evidence of active star formation by accretion in M8.Comment: 22 pages, 15 figures, 3 tables, submitted to MNRAS. A preprint with
high-resolution figures is available at
http://www.dfuls.cl/~rbarba/arias_hourglass.pd
The eccentric short-period orbit of the supergiant fast X-ray transient HD 74194 (=LM Vel)
Aims. We present the first orbital solution for the O-type supergiant star HD
74194, which is the optical counterpart of the supergiant fast X-ray transient
IGR J08408-4503. Methods. We measured the radial velocities in the optical
spectrum of HD 74194, and we determined the orbital solution for the first
time. We also analysed the complex H{\alpha} profile. Results. HD 74194 is a
binary system composed of an O-type supergiant and a compact object in a
short-period ( d) and high-eccentricity ()
orbit. The equivalent width of the H{\alpha} line is not modulated entirely
with the orbital period, but seems to vary in a superorbital period
( d) nearly 30 times longer than the orbital one.Comment: 4 pages, 6 figures, accepted for publication in A&
The Galactic O-Star Spectroscopic Survey (GOSSS). II. Bright Southern Stars
We present the second installment of GOSSS, a massive spectroscopic survey of
Galactic O stars, based on new homogeneous, high signal-to-noise ratio, R ~
2500 digital observations from both hemispheres selected from the Galactic
O-Star Catalog (GOSC). In this paper we include bright stars and other objects
drawn mostly from the first version of GOSC, all of them south of delta = -20
degrees, for a total number of 258 O stars. We also revise the northern sample
of paper I to provide the full list of spectroscopically classified Galactic O
stars complete to B = 8, bringing the total number of published GOSSS stars to
448. Extensive sequences of exceptional objects are given, including the early
Of/WN, O Iafpe, Ofc, ON/OC, Onfp, Of?p, and Oe types, as well as
double/triple-lined spectroscopic binaries. The new spectral subtype O9.2 is
also discussed. The magnitude and spatial distributions of the observed sample
are analyzed. We also present new results from OWN, a multi-epoch
high-resolution spectroscopic survey coordinated with GOSSS that is assembling
the largest sample of Galactic spectroscopic massive binaries ever attained.
The OWN data combined with additional information on spectroscopic and visual
binaries from the literature indicate that only a very small fraction (if any)
of the stars with masses above 15-20 M_Sol are born as single systems. In the
future we will publish the rest of the GOSSS survey, which is expected to
include over 1000 Galactic O stars.Comment: 110 pages, 16 figures, accepted for publication in ApJS. Some figures
have low quality due to arXiv file size limitations, alternative version
available at http://jmaiz.iaa.es/files/Sotaetal14.pd
Spectroscopic and photometric analysis of the early-type spectroscopic binary HD 161853 in the centre of an H II region
We study the O-type star HD 161853, which has been noted as a probable
double-lined spectroscopic binary system. We secured high-resolution spectra of
HD 161853 during the past nine years. We separated the two components in the
system and measured their respective radial velocities for the first time. We
confirm that HD 161853 is an 1 Ma old binary system consisting of an O8 V
star ( M) and a B1--3 V star ( M) at about 1.3 kpc. From the radial velocity curve, we measure an
orbital period = 2.667650.00001 d and an eccentricity =
0.1210.007. Its -band light curve is constant within 0.014 mag and does
not display eclipses, from which we impose a maximum orbital inclination
deg. HD 161853 is probably associated with an H II region and a poorly
investigated very young open cluster. In addition, we detect a compact emission
region at 50 arcsec to HD 161853 in 22m-WISE and 24m-Spitzer images,
which may be identified as a dust wave piled up by the radiation pressure of
the massive binary system.Comment: 5 pages, 4 figures, to appear in A&
Broad Balmer Wings in BA Hyper/Supergiants Distorted by Diffuse Interstellar Bands: Five Examples in the 30 Doradus Region from the VLT-FLAMES Tarantula Survey
Extremely broad emission wings at Hβ and Hα have been found in VLT-FLAMES Tarantula Survey data for five very luminous BA supergiants in or near 30 Doradus in the Large Magellanic Cloud. The profiles of both lines are extremely asymmetrical, which we have found to be caused by very broad diffuse interstellar bands (DIBs) in the longward wing of Hβ and the shortward wing of Hα. These DIBs are well known to interstellar but not to many stellar specialists, so that the asymmetries may be mistaken for intrinsic features. The broad emission wings are generally ascribed to electron scattering, although we note difficulties for that interpretation in some objects. Such profiles are known in some Galactic hyper/supergiants and are also seen in both active and quiescent Luminous Blue Variables (LBVs). No prior or current LBV activity is known in these 30 Dor stars, although a generic relationship to LBVs is not excluded; subject to further observational and theoretical investigation, it is possible that these very luminous supergiants are approaching the LBV stage for the first time. Their locations in the HRD and presumed evolutionary tracks are consistent with that possibility. The available evidence for spectroscopic variations of these objects is reviewed, while recent photometric monitoring does not reveal variability. A search for circumstellar nebulae has been conducted, with an indeterminate result for one of them
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