46 research outputs found
The list of the stars from the Two-micron sky survey: A preliminary catalog by G. N. Neugebauer et al (IRC), the identification of which is not correct
Two tables are published. The first presents the numbers of stars according to the Catalog IRC for which all or part of the identification with the Catalogs BS-HR, GC or DM is incorrect. The second table presents the numbers of stars in the IRC catalog, for which the identifications with variable stars printed with them are erroneous, whereas other identifications are usually correct
The new identifications of the variable stars with the stars from the ""Two-Micron Sky Survey: A Preliminary Catalog'' by G. Neugebauer etal. (IRC)
A list of 151 variable stars is presented. The identification of 148 of them is beyond any doubt. The identification of 3 stars is quite probable, but requires further checking
Some Systematics of Galactic Globular Clusters
The global properties of all known Galactic globular clusters are examined.
The relationship between the luminosities and the metallicities of Galactic
globular clusters is found to be complex. Among luminous clusters there is a
correlation in the sense that the oldest clusters are slightly more metal
deficient than are younger clusters. However, no such clear-cut relationship is
found among the faintest globular clusters. The central concentration index C
of globular clusters is seen to be independent of metallicity. The dependence
of the half-light radii of globular clusters on their Galactocentric distances
can be approximated by the relation . Clusters with
collapsed cores are mostly situated close to the Galactic nucleus. For kpc the luminosities and the radii of clusters appear to be uncorrelated.
The Galaxy differs from the LMC and the SMC in that it appears to lack highly
flattened luminous clusters. Galactic globular clusters with ages 13.0
Gyr are all of Oosterhoff type II, whereas almost all of those with ages
13.0 Gyr have been assigned to Oosterhoff type I. Globular clusters with ages
11.5 Gyr are all located in the outer Galactic halo, have below-average
luminosities and above-average radii. On the other hand the very old globular
cluster NGC 6522 is situated close to the Galactic nucleus.Comment: PASP, in pres
HST/FOS Eclipse Observations of the Nova-like Cataclysmic Variable UX Ursae Majoris
[abridged abstract]
We present and analyze Hubble Space Telescope observations of the eclipsing
nova-like cataclysmic variable UX UMa obtained with the Faint Object
Spectrograph. Two eclipses each were observed with the G160L grating (covering
the ultraviolet waveband) in August of 1994 and with the PRISM (covering the
near-ultraviolet to near-infrared) in November of the same year. The system was
50% brighter in November than in August, which, if due to a change in the
accretion rate, indicates a fairly substantial increase in Mdot_acc by >~ 50%.
Model disk spectra constructed as ensembles of stellar atmospheres provide
poor descriptions of the observed post-eclipse spectra, despite the fact that
UX UMa's light should be dominated by the disk at this time. Suitably scaled
single temperature model stellar atmospheres with T_eff = 12,500-14,500 K
actually provide a better match to both the ultraviolet and optical
post-eclipse spectra. Evidently, great care must be taken in attempts to derive
accretion rates from comparisons of disk models to observations.
One way to reconcile disk models with the observed post-eclipse spectra is to
postulate the presence of a significant amount of optically thin material in
the system. Such an optically thin component might be associated with the
transition region (``chromosphere'') between the disk photosphere and the fast
wind from the system, whose presence has been suggested by Knigge & Drew
(1997).Comment: 35 pages, including 12 figures; to appear in the ApJ (Vol. 499
The Disappearing Act of KH 15D: Photometric Results from 1995 to 2004
We present results from the most recent (2002-2004) observing campaigns of
the eclipsing system KH 15D, in addition to re-reduced data obtained at Van
Vleck Observatory (VVO) between 1995 and 2000. Phasing nine years of
photometric data shows substantial evolution in the width and depth of the
eclipses. The most recent data indicate that the eclipses are now approximately
24 days in length, or half the orbital period. These results are interpreted
and discussed in the context of the recent models for this system put forward
by Winn et al. and Chiang & Murray-Clay. A periodogram of the entire data set
yields a highly significant peak at 48.37 +/- 0.01 days, which is in accord
with the spectroscopic period of 48.38 +/- 0.01 days determined by Johnson et
al. Another significant peak, at 9.6 days, was found in the periodogram of the
out-of-eclipse data at two different epochs. We interpret this as the rotation
period of the visible star and argue that it may be tidally locked in
pseudosynchronism with its orbital motion. If so, application of Hut's theory
implies that the eccentricity of the orbit is e = 0.65 +/- 0.01. Analysis of
the UVES/VLT spectra obtained by Hamilton et al. shows that the v sin(i) of the
visible star in this system is 6.9 +/- 0.3 km/sec. Using this value of v sin(i)
and the measured rotation period of the star, we calculate the lower limit on
the radius to be R = (1.3 +/- 0.1), R_Sun, which concurs with the value
obtained by Hamilton et al. from its luminosity and effective temperature. Here
we assume that i = 90 degrees since it is likely that the spin and orbital
angular momenta vectors are nearly aligned.Comment: 55 pages, 18 figures, 1 color figure, to appear the September issue
of the Astronomical Journa
The origin of intergalactic thermonuclear supernovae
The population synthesis method is used to study the possibility of
explaining the appreciable fraction (20^+12_15%) of the intergalactic (no-host)
type Ia supernovae observed in galaxy clusters (Gal-Yam ete al. 2003) by binary
whote dwarf merginngs in the cores of globular clusters. In a typical globular
cluster, the number of merging double white dwarfs is fount to be smaller than
10^{-13} per year per average cluster star during the entire evolution of the
cluster, which is a factor of 3 higher than in a Milky-Way-type galaxy. From 5
to 30% of the merging white dwarfs are dynamically expelled from the cluster
with barycenter velocities up to 150 km/s. SN Ia explosions during the mergers
of binary white dwarfs in dense star clusters may account for \sim 1% of the
total rate of SN Ia in the central parts of galaxy clusters if the baryon mass
fraction in such star clusters is \sim 0.3%.Comment: 8 pages, 3 figs. Astronomy Letters (in press
A Photometric Survey for Variables and Transits in the Field of Praesepe with KELT
The Kilodegree Extremely Little Telescope (KELT) project is a small aperture,
wide-angle search for planetary transits of solar-type stars. In this paper, we
present the results of a commissioning campaign with the KELT telescope to
observe the open cluster Praesepe for 34 nights in early 2005. Lightcurves were
obtained for 69,337 stars, out of which we identify 58 long period variables
and 152 periodic variables. Sixteen of these are previously known as variable,
yielding 194 newly discovered variable stars for which we provide properties
and lightcurves. We also searched for planetary-like transits, finding four
transit candidates. Follow-up observations indicate that two of the candidates
are astrophysical false positives, with two candidates remaining as potential
planetary transits.Comment: 45 pages, 16 figures. Submitted to AJ. PDF version with full
resolution figures located at
http://www.astronomy.ohio-state.edu/~pepper/kelt.pd
The Period Changes of the Cepheid RT Aurigae
Observations of the light curve for the 3.7-day Cepheid RT Aur both before
and since 1980 indicate that the variable is undergoing an overall period
increase, amounting to +0.082 +-0.012 s/yr, rather than a period decrease, as
implied by all observations prior to 1980. Superposed on the star's O-C
variations is a sinusoidal trend that cannot be attributed to random
fluctuations in pulsation period. Rather, it appears to arise from light travel
time effects in a binary system. The derived orbital period for the system is P
= 26,429 +-89 days (72.36 +-0.24 years). The inferred orbital parameters from
the O-C residuals differ from those indicated by existing radial velocity data.
The latter imply the most reasonable results, namely a1 sin i = 9.09 (+-1.81) x
10^8 km and a minimum secondary mass of M2 = 1.15 +-0.25 Msun. Continued
monitoring of the brightness and radial velocity changes in the Cepheid are
necessary to confirm the long-term trend and to provide data for a proper
spectroscopic solution to the orbit.Comment: Accepted for publication in PASP (November 2007
Radio Measurements of the stellar proper motions in the core of the Orion Nebula Cluster
Sergio A. Dzib, et al, 'RADIO MEASUREMENTS OF THE STELLAR PROPER MOTIONS IN THE CORE OF THE ORION NEBULA CLUSTER', The Astrophysical Journal, Vol. 834(2), 10 pp, January 2017. doi:10.3847/1538-4357/834/2/139 © 2017. The American Astronomical Society. All rights reserved.Using multi-epoch VLA observations, covering a time baseline of 29.1 years, we have measured the proper motions of 88 young stars with compact radio emission in the core of the Orion Nebula Cluster (ONC) and the neighboring BN/KL region. Our work increases the number of young stars with measured proper motion at radio frequencies by a factor of 2.5 and enables us to perform a better statistical analysis of the kinematics of the region than was previously possible. Most stars (79 out of 88) have proper motions consistent with a Gaussian distribution centered on , and , with velocity dispersions of . We looked for organized movements of these stars but found no clear indication of radial expansion/contraction or rotation. The remaining nine stars in our sample show peculiar proper motions that differ from the mean proper motions of the ONC by more than 3-. One of these stars, V 1326 Ori, could have been expelled from the Orion Trapezium 7,000 years ago. Two could be related to the multi-stellar disintegration in the BN/KL region, in addition to the previously known sources BN, I and n. The others either have high uncertainties (so their anomalous proper motions are not firmly established) or could be foreground objects.Peer reviewedFinal Published versio
Optical Imaging of Nova Shells and the Maximum Magnitude-Rate of Decline Relationship
An optical imaging study of recent 30 novae has been undertaken using both
ground-based and space-based observations. Resolved shells have been detected
around 9 objects in the ground-based data, while another four objects have
shells detected by HST observations; for RW UMi, we fail to detect a shell
which was observed five years earlier. Images in H-alpha, and when appropriate
[O III], are shown, and finding charts for novae without shells are given if no
published chart is available. Expansion parallaxes for all systems with shells
are derived, and absolute magnitudes for a total of 28 objects are presented,
along with a discussion of the maximum magnitude-rate of decline relation. We
find that separate linear fits for fast and slow novae may be a better
representation of the data than a single, global fit. At minimum, most novae
have similar magnitudes as those of dwarf novae at maximum and novalike stars.Comment: 39 pages, 5 ps-figures, 13 jpg-figures. Accepted for publication in
the Astronomical Journal (October 2000