482 research outputs found
Central Stars of Planetary Nebulae: New spectral classifications and catalogue
Context. There are more than 3000 true and probable known Galactic Planetary
Nebulae (PNe), but only for 13% of them there is central star spectroscopic
information available. Aims. To contribute to the knowledge of central stars of
planetary nebulae and star evolution. Methods. We undertook a spectroscopic
survey of central stars of PNe in low resolution and compiled a large list of
central stars for which information was dispersed in the literature. Results.
We complete a catalogue of 492 true and probable CSPN and we provide a
preliminary spectral classification for 45 central star of PNe, This made it
possible to update the proportion of CSPN with atmosphere poor in hydrogen with
regard to the whole in at least 30% and contribute with statistical information
that allow to infer the origin of H-poor stars.Comment: 19 pages, 1 figure, accepted to be published in A&A (October 24,
2010
Improved spectral descriptions of planetary nebulae central stars
Context. At least 492 central stars of Galactic planetary nebulae (CSPNs)
have been assigned spectral types. Since many CSPNs are faint, these
classification efforts are frequently made at low spectral resolution. However,
the stellar Balmer absorption lines are contaminated with nebular emission;
therefore in many cases a low-resolution spectrum does not enable the
determination of the H abundance in the CSPN photosphere. Whether or not the
photosphere is H deficient is arguably the most important fact we should expect
to extract from the CSPN spectrum, and should be the basis for an adequate
spectral classification system.
Aims. Our purpose is to provide accurate spectral classifications and
contribute to the knowledge of central stars of planetary nebulae and stellar
evolution.
Methods. We have obtained and studied higher quality spectra of CSPNs
described in the literature as weak emission-line star (WELS). We provide
descriptions of 19 CSPN spectra. These stars had been previously classified at
low spectral resolution. We used medium-resolution spectra taken with the
Gemini Multi-Object Spectrograph (GMOS). We provide spectral types in the
Morgan-Keenan (MK) system whenever possible.
Results. Twelve stars in our sample appear to have normal H rich photospheric
abundances, and five stars remain unclassified. The rest (two) are most
probably H deficient. Of all central stars described by other authors as WELS,
we find that at least 26% of them are, in fact, H rich O stars, and at least 3%
are H deficient. This supports the suggestion that the denomination WELS should
not be taken as a spectral type, because, as a WELS based on low-resolution
spectra, it cannot provide enough information about the photospheric H
abundance.Comment: Accepted to be published in the A&
Apsidal motion in massive close binary systems. I. HD 165052 an extreme case?
We present a new set of radial-velocity measurements of the spectroscopic
binary HD 165052 obtained by disentangling of high-resolution optical spectra.
The longitude of the periastron (60 +- 2 degrees) shows a variation with
respect to previous studies. We have determined the apsidal motion rate of the
system (12.1 +- 0.3 degree/yr), which was used to calculate the absolute masses
of the binary components: M_1 = 22.5 +- 1.0 and M_2 = 20.5 +- 0.9 solar masses.
Analysing the separated spectra we have re-classified the components as O7Vz
and O7.5Vz stars
Stellar populations in the Carina region: The Galactic plane at l = 291
Previous studies of the Carina region have revealed its complexity and
richness as well as a significant number of early-type stars. In many cases,
these studies only concentrated on the central region or were not homogeneous.
This latter aspect, in particular, is crucial because very different ages and
distances for key clusters have been claimed in recent years. The aim of this
work is to study in detail an area of the Galactic plane in Carina. We analyze
the properties of different stellar populations and focus on a sample of open
clusters and their population of YSOs and highly reddened early stars. We also
studied the stellar mass distribution in these clusters and the possible
scenario of their formation. Finally, we outline the Galactic spiral structure
in this direction. We obtained photometric data for six young open clusters
located in Carina at l = 291, and their adjacent stellar fields, which we
complemented with spectroscopic observations of a few selected targets. We also
culled additional information from the literature. Our results provide more
reliable estimates of distances, color excesses, masses, and ages of the
stellar populations in this direction. We estimate the basic parameters of the
studied clusters and find that they identify two overdensities of young stellar
populations. We find evidence of PMS populations inside them, with an apparent
coeval stellar formation in the most conspicuous clusters. We also discuss
apparent age and distance gradients in the direction NW-SE. We study the mass
distributions of several clusters in the region. They consistently show a
canonical IMF slope. We discover and characterise an abnormally reddened
massive stellar population. Spectroscopic observations of ten stars of this
latter population show that all selected targets were massive OB stars. Their
location is consistent with the position of the Car-Sag spiral arm.Comment: 15 pages, 13 figure
Central Stars of Galactic Planetary Nebulae II New OB-type and emission-line stars
Context. There are more than 3000 confirmed and probable known Galactic
planetary nebulae, but central star spectroscopic information is available for
only 13% of them. Aims. We undertook a spectroscopic survey of central stars of
PNe to identify their spectral types. Methods. We performed spectroscopic
observations, at low resolution, with the 2-m telescope at CASLEO, Argentina.
Results. We present the spectra of 46 central stars of PNe, most of them are
OB-type and emission-line stars.Comment: 13 pages, 13 figures, accepted to be published in A&A (May 30, 2011
Discovery of a deep Seyfert-2 galaxy at z = 0.222 behind NGC 300
We report on the unveiling of the nature of the unidentified X-ray source
3XMM J005450.3-373849 as a Seyfert-2 galaxy located behind the spiral galaxy
NGC 300 using Hubble Space Telescope data, new spectroscopic Gemini
observations and available XMM-Newton and Chandra data. We show that the X-ray
source is positionally coincident with an extended optical source, composed by
a marginally resolved nucleus/bulge, surrounded by an elliptical disc-like
feature and two symmetrical outer rings. The optical spectrum is typical of a
Seyfert-2 galaxy redshifted to z=0.222 +/- 0.001, which confirms that the
source is not physically related to NGC 300. At this redshift the source would
be located at 909+/-4 Mpc (comoving distance in the standard model). The X-ray
spectra of the source are well-fitted by an absorbed power-law model. By tying
between the six available spectra, we found a variable index
running from ~2 in 2000-2001 years, to 1.4-1.6 in the 2005-2014
period. Alternatively, by tying , we found variable absorption columns
of N_H ~ 0.34 x cm in 2000-2001 years, and 0.54-0.75 x
cm in the 2005-2014 period. Although we cannot distinguish
between an spectral or absorption origin, from the derived unabsorbed X-ray
fluxes, we are able to assure the presence of long-term X-ray variability.
Furthermore, the unabsorbed X-ray luminosities of 0.8-2 x 10 erg
s derived in the X-ray band are in agreement with a weakly obscured
Seyfert-2 AGN at .Comment: MNRAS, accepte
Triggered star formation in a molecular shell created by a SNR?
We present a study of a new molecular shell, G126.1-0.8-14, using available
multiwavelegth Galactic plane surveys and optical Gemini observations. A well
defined shell-like structure is observed in the CO(1--0) line emission at (l,b)
= (126.1, -0.8), in the velocity range --10.5 to --15.5 km/s. The HI, emission
shows a region of low emissivity inside G126.1-0.8-14, while radio continuum
observations reveal faint non-thermal emission possibly related to this shell.
Optical spectra obtained with Gemini South show the existence of B-type stars
likely to be associated with G126.1-0.8-14. An estimate of the stellar wind
energy injected by these stars show that they alone can not be able to create
such a structure. On the other hand, one supernova explosion would provide
enough energy to generate the shell. Using the MSX, IRAS, and WISE Point Source
Catalogues we have found about 30 young stellar objects candidates, whose birth
could have been triggered by the expansion of G126.1-0.8-14. In this context,
Sh2-187 could be a consequence of the action on its surroundings of the most
massive (and thus most evolve) of the stars formed by the expanding molecular
shell.Comment: 13 pages, 10 figures, accepted in MNRA
Central stars of planetary nebulae: New spectral classifications and catalogue
Context. There are more than 3000 confirmed and probable known Galactic planetary nebulae (PNe), but central star spectroscopic information is available for only 13% of them. Aims. We undertook a spectroscopic survey of central stars of PNe at low resolution and compiled a large list of central stars for which information was dispersed in the literature. Methods. We observed 45 PNs using the 2.15 m telescope at Casleo, Argentina. Results. We present a catalogue of 492 confirmed and probable CSPN and provide a preliminary spectral classification for 45 central star of PNe. This revises previous values of the proportion of CSPN with atmospheres poor in hydrogen in at least 30% of cases and provide statistical information that allows us to infer the origin of H-poor stars.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica
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