185 research outputs found
Searches for the Shell Swept up by the Stellar Wind from Cyg OB2
We investigated the kinematics of ionized gas in an extended (20 degrees by
15 degrees) region containing the X-ray Superbubble in Cygnus with the aim of
finding the shell swept up by a strong wind from Cyg OB2. H-alpha observations
were carried out with high angular and spectral resolutions using a Fabry-Perot
interferometer attached to the 125-cm telescope at the Crimean Observatory of
the Sternberg Astronomical Institute. We detected high-velocity gas motions,
which could result from the expansion of the hypothetical shell at a velocity
of 25-50 km/s. Given the number of OB stars increased by Knoedlseder (2000) by
an order of magnitude, Cyg OB2 is shown to possess a wind that is strong enough
[Lw ~= (1-2)x10^39 erg/s] to produce a shell comparable in size to the X-ray
Superbubble and to a giant system of optical filaments. Based on our
measurements and on X-ray and infrared observations, we discuss possible
observational manifestations of the shell swept up by the wind.Comment: 14 pages, Astronomy Letter
Multi-color Classification in the Calar Alto Deep Imaging Survey
We use a multi-color classification method introduced by Wolf, Meisenheimer &
Roeser (2000) to reliably identify stars, galaxies and quasars in the up to
16-dimensional color space provided by the filter set of the Calar Alto Deep
Imaging Survey (CADIS). The samples of stars, galaxies and quasars obtained
this way have been used for dedicated studies published in separate papers. The
classification is good enough to detect quasars rather completely and
efficiently without confirmative spectroscopy. The multi-color redshifts are
accurate enough for most statistical applications, e.g. evolutionary studies of
the galaxy luminosity function. We characterize our current dataset on the
CADIS 1h-, 9h- and 16h-fields. Using Monte-Carlo simulations we model the
classification performance expected for CADIS. We present a summary of the
classification results and discuss unclassified objects. More than 99% of the
whole catalog sample at R<22 (more than 95% at R<23) are successfully
classified matching the expectations derived from the simulations. A small
number of peculiar objects challenging the classification are discussed in
detail. Spectroscopic observations are used to check the reliability of the
multi-color classification (6 mistakes among 151 objects with R<24). We also
determine the accuracy of the multi-color redshifts which are rather good for
galaxies (sigma_z = 0.03) and useful for quasars. We find the classification
performance derived from the simulations to compare well with results from the
real survey. Finally, we locate areas for potential improvement of the
classification.Comment: 18 pages, 13 figures included, accepted for publication in Astronomy
& Astrophysic
Multi-color classification in the calar alto deep imaging survey
We use a multi-color classification method introduced by Wolf et al. ([CITE]) to reliably identify stars, galaxies and quasars in the up to 16-dimensional color space provided by the filter set of the Calar Alto Deep Imaging Survey (CADIS). The samples of stars, galaxies and quasars obtained this way have been used for dedicated studies which are published in separate papers. The classification is good enough to detect quasars rather completely and efficiently without confirmative spectroscopy. The multi-color redshifts are accurate enough for most statistical applications, e.g. evolutionary studies of the galaxy luminosity function. Also, the separation between stars and galaxies reaches deeper than with morphological criteria, so that studies of the stellar population can be extended to fainter levels. We characterize the dataset presently available on the CADIS 1 h-, 9 h- and 16 h-fields. Using Monte-Carlo simulations we model the classification performance expected for CADIS. We present a summary of the classification results on the CADIS database and discuss unclassified objects. More than 99% of the whole catalog sample at R < 22 (more than 95% at R < 23) are successfully classified matching the expectations derived from the simulations. A small number of peculiar objects challenging the classification is discussed in detail. Spectroscopic observations are used to check the reliability of the multi-color classification (6 mistakes among 151 objects with R < 24). From these, we also determine the accuracy of the multi-color redshifts which are rather good for galaxies (σ_z ≈ 0.03) and useful for quasars. We find that the classification performance derived from the simulations compares well with results from the real survey. Finally, we locate areas for potential improvement of the classification
High resolution optical spectroscopy of an LBV-candidate inside the CygOB2 association
For the first time, we obtained the high-resolution (R=15000 and 60000)
optical spectra for the extremely luminous star No.12, associated with the
IR-source IRAS20308+4104, a member of the CygOB2 association. We have found
about 200 spectral features in range 4552-7939AA, including the interstellar
NaI, KI lines and numerous DIBs, which are the strongest absorption lines in
the spectrum, along with the HeI, CII, and SiII lines. A two-dimensional
spectral classification indicates that the spectral type is B5+/-0.5 Ia+. Our
analysis of the Vr data shows the presence of a Vr gradient in the stellar
atmosphere, caused by the infall of matter onto the star. The strong Halpha
emission displays broad Thompson wings and time-variable core absorption,
providing evidence that the stellar wind is inhomogeneous, and a slightly
blue-shifted PCyg type absorption profile. We concluded that the wind is
variable in time.Comment: 20 pages, 5 figures, 2 table
The Chandra Multiwavelength Project: Optical Followup of Serendipitous Chandra Sources
We present followup optical g', r', and i', imaging and spectroscopy of
serendipitous X-ray sources detected in 6 archival Chandra, images included in
the Chandra, Multiwavelength Project (ChaMP). Of the 486 X-ray sources detected
between 3e-16 and 2e-13 (with a median flux of 3e-15 erg cm-2 s-1, we find
optical counterparts for 377 (78%), or 335 (68%) counting only unique
counterparts. We present spectroscopic classifications for 125 objects,
representing 75% of sources with r<21 optical counterparts (63% to r=22). Of
all classified objects, 63 (50%) are broad line AGN, which tend to be blue in
g-r colors. X-ray information efficiently segregates these quasars from stars,
which otherwise strongly overlap in these SDSS colors until z>3.5. We identify
28 sources (22%) as galaxies that show narrow emission lines, while 22 (18%)
are absorption line galaxies. Eight galaxies lacking broad line emission have
X-ray luminosities that require they host an AGN (logL_X>43). Half of these
have hard X-ray emission suggesting that high gas columns obscure both the
X-ray continuum and the broad emission line regions. We find objects in our
sample that show signs of X-ray or optical absorption, or both, but with no
strong evidence that these properties are coupled. ChaMP's deep X-ray and
optical imaging enable multiband selection of small and/or high-redshift groups
and clusters. In these 6 fields we have discovered 3 new clusters of galaxies,
two with z>0.4, and one with photometric evidence that it is at a similar
redshift.Comment: 38 pages, Latex, emulateapj style, including 6 tables and 22 figures.
Accepted Aug 24, 2003 for publication in ApJ Supplement. See accompanying
X-ray papers by Kim et al. 2003 and the ChaMP web site at
http://hea-www.harvard.edu/CHAMP
The Lyman Alpha Forest in the Spectra of QSOs
Observations of redshifted Lyman alpha forest absorption in the spectra of
quasistellar objects (QSOs) provide a highly sensitive probe of the
distribution of gaseous matter in the universe. Over the past two decades
optical spectroscopy with large ground-based telescopes, and more recently
ultraviolet spectroscopy from space have yielded a wealth of information on
what appears to be a gaseous, photoionized intergalactic medium, partly
enriched by the products of stellar nucleosynthesis, residing in coherent
structures over many hundreds of kiloparsecs. Recent progress with cosmological
hydro-simulations based on hierarchical structure formation models has led to
important insights into the physical structures giving rise to the forest. If
these ideas are correct, a truely inter- and proto-galactic medium [at high
redshift (z ~ 3), the main repository of baryons] collapses under the influence
of dark matter gravity into flattened or filamentary structures, which are seen
in absorption against background QSOs. With decreasing redshift, galaxies
forming in the denser regions, may contribute an increasing part of the Lyman
alpha absorption cross-section. Comparisons between large data samples from the
new generation of telescopes and artificial Lyman alpha forest spectra from
cosmological simulations promise to become a useful cosmological tool.Comment: latex plus three postscript figures, uses psfig,sty; Annual Review of
Astronomy and Astrophysics 1998, vol. 36 (in press
Female chromosome X mosaicism is age-related and preferentially affects the inactivated X chromosome
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