7 research outputs found
VLBA determination of the distance to nearby star-forming regions I. The distance to T Tauri with 0.4% accuracy
In this article, we present the results of a series of twelve 3.6-cm radio
continuum observations of T Tau Sb, one of the companions of the famous young
stellar object T Tauri. The data were collected roughly every two months
between September 2003 and July 2005 with the Very Long Baseline Array (VLBA).
Thanks to the remarkably accurate astrometry delivered by the VLBA, the
absolute position of T Tau Sb could be measured with a precision typically
better than about 100 micro-arcseconds at each of the twelve observed epochs.
The trajectory of T Tau Sb on the plane of the sky could, therefore, be traced
very precisely, and modeled as the superposition of the trigonometric parallax
of the source and an accelerated proper motion. The best fit yields a distance
to T Tau Sb of 147.6 +/- 0.6 pc. The observed positions of T Tau Sb are in good
agreement with recent infrared measurements, but seem to favor a somewhat
longer orbital period than that recently reported by Duchene et al. (2006) for
the T Tau Sa/T Tau Sb system.Comment: 24 pages, 3 pages, AASTEX format, accepted for publication in Ap
WFPC2 Observations of the Hubble Deep Field-South
The Hubble Deep Field-South observations targeted a high-galactic-latitude
field near QSO J2233-606. We present WFPC2 observations of the field in four
wide bandpasses centered at roughly 300, 450, 606, and 814 nm. Observations,
data reduction procedures, and noise properties of the final images are
discussed in detail. A catalog of sources is presented, and the number counts
and color distributions of the galaxies are compared to a new catalog of the
HDF-N that has been constructed in an identical manner. The two fields are
qualitatively similar, with the galaxy number counts for the two fields
agreeing to within 20%. The HDF-S has more candidate Lyman-break galaxies at z
> 2 than the HDF-N. The star-formation rate per unit volume computed from the
HDF-S, based on the UV luminosity of high-redshift candidates, is a factor of
1.9 higher than from the HDF-N at z ~ 2.7, and a factor of 1.3 higher at z ~ 4.Comment: 93 pages, 25 figures; contains very long table
Spectroscopy of NGC 4258 Globular Cluster Candidates:Membership Confirmation and Kinematics
We present multi-object spectroscopic observations of 23 globular cluster
candidates (GCCs) in the prototypical megamaser galaxy NGC 4258, carried out
with the OSIRIS instrument at the 10.4 m Gran Telescopio Canarias. The
candidates have been selected based on the () versus
() diagram, in the first application of the uiks-method to a
spiral galaxy. In the spectroscopy presented here, 70% of the candidates are
confirmed as globular clusters. Our results validate the efficiency of the
uiks-method in the sparser GC systems of spirals, and given the downward
correction to the total number of GCs, the agreement of the galaxy with the
correlations between black hole mass, and total number and mass of GCs is
actually improved. We find that the GCs, mostly metal-poor, co-rotate with the
HI disk, even at large galactocentric distances.Comment: 25 pages, 15 figures; accepted for publication in The Astrophysical
Journa