7,919 research outputs found
Photometric and spectroscopic variability of the FUor star V582 Aurigae
We carried out BVRI CCD photometric observations in the field of V582 Aur
from 2009 August to 2013 February. We acquired high-, medium-, and
low-resolution spectroscopy of V582 Aur during this period. To study the
pre-outburst variability of the target and construct its historical light
curve, we searched for archival observations in photographic plate collections.
Both CCD and photographic observations were analyzed using a sequence of 14
stars in the field of V582 Aur calibrated in BVRI. The pre-outburst
photographic observations of V582 Aur show low-amplitude light variations
typical of T Tauri stars. Archival photographic observations indicate that the
increase in brightness began in late 1984 or early 1985 and the star reached
the maximum level of brightness at 1986 January. The spectral type of V582 Aur
can be defined as G0I with strong P Cyg profiles of H alpha and Na I D lines,
which are typical of FU Orionis objects. Our BVRI photometric observations show
large amplitude variations V~2.8 mag. during the 3.5 year period of
observations. Most of the time, however, the star remains in a state close to
the maximum brightness. The deepest drop in brightness was observed in the
spring of 2012, when the brightness of the star fell to a level close to the
pre-outburst. The multicolor photometric data show a color reversal during the
minimum in brightness, which is typical of UX Ori variables. The corresponding
spectral observations show strong variability in the profiles and intensities
of the spectral lines (especially H alpha), which indicate significant changes
in the accretion rate. On the basis of photometric monitoring performed over
the past three years, the spectral properties of the maximal light, and the
shape of the long-term light curve, we confirm the affiliation of V582 Aur to
the group of FU Orionis objects.Comment: 9 pages, 8 figures, accepted for publication in A&
Spectroscopic and physical parameters of Galactic O-type stars. I. Effects of rotation and spectral resolving power in the spectral classification of dwarfs and giants
The modern-era spectral classification of O-stars relies on either the
Walborn or the Conti-Mathys scheme. Since both of these approaches have been
developed using low-quality photographic data, their application to
high-quality digital data might not be straightforward and be hampered by
problems and complications that have not yet been appreciated. Using
high-resolution spectra obtained with the ESO/MPG 2.2\,m telescope in La Silla
and following the premises of the Walborn and Conti classification schemes, we
determined the spectral types and luminosity classes of 19 Galactic O-type
stars and compared them to those attributed by Walborn and Mathys based on
low-quality data. Our analysis reveals that the morphological spectral types
assigned using high-resolution data are systematically later (by up to 1.5
subtypes) then those attributed by Walborn. By means of line-profile
simulations, we show that part of this discrepancy is more likely caused by the
combined effect of stellar rotation and high spectral resolution on the depth
of helium lines used as spectral type indicators. In addition, we demonstrate
that at least for narrow-lined stars the "rotational effect" does not disappear
when the high-resolution spectra are degraded to the resolution of the Walborn
standards. We also find evidence of a systematic difference between our
high-resolution quantitative spectral types and those assigned by Mathys.
Rotation and spectral resolution are important third parameters in the spectral
classification of O-type stars. To obtain reliable spectral classes within the
Walborn approach, the unknown and the standard spectra must be compared at the
same resolution and \vsini. Owing to resolution effects, the Conti approach
might also need to be updated.Comment: paper accepted for publication in A&
LSS 1135: an O-Type Spectroscopic Binary in the galactic OB association Bochum 7
From radial velocities derived from optical spectroscopic observations
performed at CTIO, Chile, and CASLEO, Argentina, we have discovered that LSS
1135 is a single--lined O-type binary system with an orbital period of 2.7532
days. We present an analysis of the orbital elements of this system based on
radial velocities of the He absorption lines. We classify the spectrum of LSS
1135 as O6.5V((f)). We also present spectral classifications and radial
velocities for other seven OB stars in the region of Bochum 7, an OB
association to which LSS 1135 belongs. Our data indicate a distance of 5.0 kpc
for this star group.Comment: 5 pages, 4 figures, many tables, uses aa.cls version 4.05. Accepted
for publication in A&
Four-colour photometry of eclipsing binaries. XLI uvby light curves for AD Bootis, HW Canis Majoris, SW Canis Majoris, V636 Centauri, VZ Hydrae, and WZ Ophiuchi
CONTEXT: Accurate mass, radius, and abundance determinations from binaries
provide important information on stellar evolution, fundamental to central
fields in modern astrophysics and cosmology.
AIMS: Within the long-term Copenhagen Binary Project, we aim to obtain
high-quality light curves and standard photometry for double-lined detached
eclipsing binaries with late A, F, and G type main-sequence components, needed
for the determination of accurate absolute dimensions and abundances, and for
detailed comparisons with results from recent stellar evolutionary models.
METHODS: Between March 1985 and July 2007, we carried out photometric
observations of AD Boo, HW CMA, SW CMa, V636 Cen, VZ Hya, and WZ Oph at the
Str"omgren Automatic Telescope at ESO, La Silla.
RESULTS: We obtained complete uvby light curves, ephemerides, and standard
uvby\beta indices for all six systems.For V636 Cen and HW CMa, we present the
first modern light curves, whereas for AD Boo, SW CMa, VZ Hya, and WZ Oph, they
are both more accurate and more complete than earlier data. Due to a high
orbital eccentricity (e = 0.50), combined with a low orbital inclination (i =
84.7), only one eclipse, close to periastron, occurs for HW CMa. For the two
other eccentric systems, V636 Cen (e = 0.134) and SW CMa (e = 0.316), apsidal
motion has been detected with periods of 5270 +/- 335 and 14900 +/- 3600 years,
respectively.Comment: Only change is: Bottom lines (hopefully) not truncated anymore.
Accepted for publication in Astonomy & Astrophysic
The Fornax Spectroscopic Survey I. Survey Strategy and Preliminary Results on the Redshift Distribution of a Complete Sample of Stars and Galaxies
The Fornax Spectroscopic Survey will use the Two degree Field spectrograph
(2dF) of the Anglo-Australian Telescope to obtain spectra for a complete sample
of all 14000 objects with 16.5<=Bj<=19.7 in a 12 square degree area centred on
the Fornax Cluster. By selecting all objects---both stars and
galaxies---independent of morphology, we cover a much larger range of surface
brightness and scale size than previous surveys. In this paper we present
results from the first 2dF field. Redshift distributions and velocity
structures are shown for all observed objects in the direction of Fornax,
including Galactic stars, galaxies in and around the Fornax Cluster, and for
the background galaxy population. The velocity data for the stars show the
contributions from the different Galactic components, plus a small tail to high
velocities. We find no galaxies in the foreground to the cluster in our 2dF
field. The Fornax Cluster is clearly defined kinematically. The mean velocity
from the 26 cluster members having reliable redshifts is 1560+/-80 km/s. They
show a velocity dispersion of 380+/-50 km/s. Large-scale structure can be
traced behind the cluster to a redshift beyond z=0.3. Background compact
galaxies and low surface brightness galaxies are found to follow the general
galaxy distribution.Comment: LaTeX format; uses aa.cls (included). Accepted for publication in
Astronomy and Astrophysic
Hubble Space Telescope Spectroscopy of the Balmer lines in Sirius B
Sirius B is the nearest and brightest of all white dwarfs, but it is very
difficult to observe at visible wavelengths due to the overwhelming scattered
light contribution from Sirius A. However, from space we can take advantage of
the superb spatial resolution of the Hubble Space Telescope to resolve the A
and B components. Since the closest approach in 1993, the separation between
the two stars has become increasingly favourable and we have recently been able
to obtain a spectrum of the complete Balmer line series for Sirius B using
HST?s Space Telescope Imaging Spectrograph (STIS). The quality of the STIS
spectra greatly exceed that of previous ground-based spectra, and can be used
to provide an important determination of the stellar temperature (Teff =
25193K) and gravity (log g = 8.556). In addition we have obtained a new, more
accurate, gravitational red-shift of 80.42 +/- 4.83 km s-1 for Sirius B.
Combining these results with the photometric data and the Hipparcos parallax we
obtain new determinations of the stellar mass for comparison with the
theoretical mass-radius relation. However, there are some disparities between
the results obtained independently from log g and the gravitational redshift
which may arise from flux losses in the narrow 50x0.2arcsec slit. Combining our
measurements of Teff and log g with the Wood (1995) evolutionary mass-radius
relation we get a best estimate for the white dwarf mass of 0.978 M. Within the
overall uncertainties, this is in agreement with a mass of 1.02 M obtained by
matching our new gravitational red-shift to the theoretical M/R relation.Comment: 11 pages, 6 figures, accepted for publication in the Monthly Notices
of the Royal Astronomical Societ
Survey for Emission-Line Galaxies: Universidad Complutense de Madrid List 3
A new low-dispersion objective-prism search for low-redshift (z<0.045)
emission-line galaxies (ELG) has been carried out by the Universidad
Complutense de Madrid with the Schmidt Telescope at the Calar-Alto Observatory.
This is a continuation of the UCM Survey, which was performed by visual
selection of candidates in photographic plates via the presence of the
Halpha+[NII]6584 blend in emission. In this new list we have applied an
automatic procedure, fully developed by us, for selecting and analyzing the ELG
candidates on the digitized images obtained with the MAMA machine. The analyzed
region of the sky covers 189 square degrees in nine fields near R.A.=14h & 17h,
Dec=25 deg. The final sample contains 113 candidates. Special effort has been
made to obtain a large amount of information directly from our uncalibrated
plates by using several external calibrations. The parameters obtained for the
ELG candidates allow for the study of the statistical properties for the
sample.Comment: 13 pages, 18 PostScript figures, 6 JPEG figures, Table 2 corrected.
Accepted for publication in Astrophysical Journal Supplements, also available
at http://www.ucm.es/info/Astrof/opera/LIST3_ApJS99
On the nature of V2282 Sgr
The star V2282 Sgr is positionally consistent with a strong Chandra X-ray and
a Spitzer/IRAC MIR source. We derived its long term -band light curve from
the photographic archives of the Asiago and Catania Observatories, covering the
years from 1965 to 1984. CCD photometry in Summer 2009 was re-analyzed.
Optical spectra were secured at Loiano Observatory in 2011 and 2012. J H K
photometry, obtained from several experiments in different epochs was compared
and the Spitzer images were re-analyzed.
V2282 Sgr was found to be irregular variable in all wavelengths.
Spectroscopically, it shows strong emission features (H Balmer lines, [NII]6584
AA and [OIII]5007/4959 AA) while the Na D doublet is very strong, indicating a
circumstellar envelope. A single thermal energy distribution cannot reproduce
the observed SED, while it can be explained as the sum of a G-type star plus a
variable circumstellar disc, which mimics a class 0/I object. Most likely,
V2282 Sgr is a 1-2 mass pre main sequence star with an accretion
disk.Comment: 13 pages, 7 figure, in press on Baltic Astronom
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