2,389 research outputs found
Tomographic Separation of Composite Spectra. IX. The Massive Close Binary HD 115071
We present the first orbital elements for the massive close binary, HD
115071, a double-lined spectroscopic binary in a circular orbit with a period
of 2.73135 +/- 0.00003 days. The orbital semiamplitudes indicate a mass ratio
of M_2/M_1 = 0.58 +/- 0.02 and yet the stars have similar luminosities. We used
a Doppler tomography algorithm to reconstruct the individual component optical
spectra, and we applied well known criteria to arrive at classifications of
O9.5 V and B0.2 III for the primary and secondary, respectively. We present
models of the Hipparcos light curve of the ellipsoidal variations caused by the
tidal distortion of the secondary, and the best fit model for a Roche-filling
secondary occurs for an inclination of i = 48.7 +/- 2.1 degrees. The resulting
masses are 11.6 +/- 1.1 and 6.7 +/- 0.7 solar masses for the primary and
secondary, respectively, so that both stars are very overluminous for their
mass. The system is one of only a few known semi-detached, Algol-type binaries
that contain O-stars. We suggest that the binary has recently emerged from
extensive mass transfer (possibly through a delayed contact and common envelope
process).Comment: Submitted to Ap
Galaxy populations in the Antlia cluster. I. Photometric properties of early-type galaxies
We present the first colour-magnitude relation (CMR) of early-type galaxies
in the central region of the Antlia cluster, obtained from CCD wide-field
photometry in the Washington photometric system. Integrated (C -T1) colours, T1
magnitudes, and effective radii have been measured for 93 galaxies (i.e. the
largest galaxies sample in the Washington system till now) from the FS90
catalogue (Ferguson & Sandage 1990). Membership of 37 objects can be confirmed
through new radial velocities and data collected from the literature. The
resulting colour-magnitude diagram shows that early-type FS90 galaxies that are
spectroscopically confirmed Antlia members or that were considered as definite
members by FS90, follow a well defined CMR (sigma_(C -T1) ~ 0.07 mag) that
spans 9 magnitudes in brightness with no apparent change of slope. This
relation is very tight for the whole magnitude range but S0 galaxies show a
larger dispersion, apparently due to a separation of ellipticals and S0s.
Antlia displays a slope of -13.6 in a T1 vs. (C -T1) diagram, in agreement with
results for clusters like Fornax, Virgo, Perseus and Coma, which are
dynamically different to Antlia. This fact might indicate that the build up of
the CMR in cluster of galaxies is more related to galaxies internal processes
than to the influence of the environment. Interpreting the CMR as a
luminosity-metallicity relation of old stellar systems, the metallicities of
the Antlia galaxies define a global relation down to Mv ~ -13. We also find,
for early-type dwarfs, no clear relation between luminosity and effective
radius, indicating a nearly constant mean effective radius of ~ 1 kpc. This
value is also found in several samples of dwarf galaxies in Virgo and Coma.Comment: 13 pages, 6 figures. Accepted for publication in MNRA
DDO Photometry of M71: Carbon and Nitrogen Patterns Among Evolving Giants
We present V, B-V, and DDO C(41-42) and C(42-45) photometry for a sample of
75 red giants down to M_V = +2 in the relatively metal-rich Galactic globular
cluster M71. The C(41-42) colors reveal a bimodal distribution of CN band
strengths generally anticorrelated with CH band strength as measured by the
C(42-45) color. Both DDO colors agree well with those found in 47 Tucanae -- a
nearby globular cluster of similar metallicity -- and suggest nearly identical
C and N abundance patterns among the giants of both clusters. A comparison with
synthetic DDO colors demonstrates that little change in surface C or N
abundance is required to match the colors of the M71 giants over the entire
luminosity range observed. Apparently like 47 Tuc (a cluster of much greater
mass and central concentration), M71 exhibits an abundance pattern which cannot
be solely the result of internal mixing.Comment: To appear in the Astronomical Journal, November 2001. 17 Pages, 5
Figure
Tomographic Separation of Composite Spectra. VIII. The Physical Properties of the Massive Compact Binary in the Triple Star System HD 36486 (delta Orionis A)
Double-lined spectroscopic orbital elements have recently been found for the
central binary in the massive triple, delta Orionis A based on radial
velocities from cross-correlation techniques applied to IUE high dispersion
spectra and He I 6678 spectra obtained at Kitt Peak. The primary and secondary
velocity amplitudes were found to be 94.9 +/- 0.6 km/s and 186 +/- 9 km/s
respectively. Tomographic reconstructions of the primary and secondary stars'
spectra confirm the O9.5 II classification of the primary and indicate a B0.5
III type for the secondary. The widths of the UV cross-correlation functions
are used to estimate the projected rotational velocities, Vsin i = 157 +/- 6
km/s and 138 +/- 16 km/s for the primary and secondary, respectively implying
that both stars rotate faster than their orbital motion. We used the
spectroscopic results to make a constrained fit of the Hipparcos light curve of
this eclipsing binary, and the model fits limit the inclination to the range
between 67 and 77 degrees. The i = 67 degrees solution, which corresponds to a
near Roche-filling configuration, results in a primary mass of 11.2 solar
masses and a secondary mass of 5.6 solar masses, both of which are
substantially below the expected masses for stars of their luminosity. This
binary may have experienced a mass ratio reversal caused by Case A Roche lobe
overflow, or the system may have suffered extensive mass loss through a binary
interaction, perhaps during a common envelope phase, in which most of the
primary's mass was lost from the system rather than transferred to the
secondary.Comment: 27 pages, 15 figures in press, the Astrophysical Journal, February 1,
200
Gas Accretion by Globular Clusters and Nucleated Dwarf Galaxies and the Formation of the Arches and Quintuplet Clusters
We consider here the collective accretion of gas by globular clusters and
dwarf galaxies moving through the interstellar medium. In the limit of high
velocity and/or sound speed of the ISM, the collective potential of the cluster
is insufficient to accrete significant amounts of gas, and stars within the
systems accrete gas individually. We show, however, that when the sound speed
or the relative velocity of the ambient medium is less than the central
velocity dispersion of the cluster, it is accreted into the collective
potential of the cluster prior to being accreted onto the individual stars
within the cluster. The collective rate is strongly enhanced relative to the
individual rates. This effect may potentially modify the white dwarf cooling
sequence in globular clusters with low-inclination and low-eccentricity
Galactic orbits, and lead to the rejuvenation of some marginally surviving
cores of globular clusters and nucleated dwarf galaxies near the Galactic
center. Such effects will only occur rarely, but may explain the existence of
clusters of young, massive stars near the Galactic center.Comment: 21 pages, 1 figure, to appear in The Astrophysical Journa
Dissociation constants and thermodynamic properties of amino acids used in CO2 absorption from (293 to 353) K
The second dissociation constants of the amino acids ĂÂČalanine, taurine, sarcosine, 6-aminohexanoic acid, DL-methionine, glycine, L-phenylalanine, and L-proline and the third dissociation constants of L-glutamic acid and L-aspartic acid have been determined from electromotive force measurements at temperatures from (293 to 353) K. Experimental results are reported and compared to literature values. Values of the standard state thermodynamic properties are derived from the experimental results and compared to the values of commercially available amines used as absorbents for CO 2 capture.
EXPORT: optical photometry and polarimetry of Vega-type and pre-main sequence stars
This paper presents optical UBVRI broadband photo-polarimetry of the EXPORT
sample obtained at the 2.5m Nordic Optical Telescope. The database consists of
multi-epoch photo-polarimetry of 68 pre-main-sequence and main-sequence stars.
An investigation of the polarization variability indicates that 22 objects are
variable at the 3sigma level in our data. All these objects are pre-main
sequence stars, consisting of both T Tauri and Herbig Ae/Be objects while the
main sequence, Vega type and post-T Tauri type objects are not variable. The
polarization properties of the variable sources are mostly indicative of the
UXOR-type behaviour; the objects show highest polarization when the brightness
is at minimum. We add seven new objects to the class of UXOR variables (BH Cep,
VX Cas, DK Tau, HK Ori, LkHa 234, KK Oph and RY Ori). The main reason for their
discovery is the fact that our data-set is the largest in its kind, indicating
that many more young UXOR-type pre-main sequence stars remain to be discovered.
The set of Vega-like systems has been investigated for the presence of
intrinsic polarization. As they lack variability, this was done using indirect
methods, and apart from the known case of BD +31.643, the following stars were
found to be strong candidates to exhibit polarization due to the presence of
circumstellar disks: 51 Oph, BD +31.643C, HD 58647 and HD 233517.Comment: A&A accepte
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