832 research outputs found
Hall station and camera system operation and maintenance manual
The major components of the Hall station and camera system are described. The Hall film record of an event provides the time of flight of the projectile between the slits. A time mark generator is used to supply extremely short pulses of light at a known frequency. These pulses of light are used to produce timing marks on the edge of the film. Comparison of these marks with the spacing of the projectile images provides the information necessary to determine the time of flight of the projectile. Since the slits are installed with a known separation distance, calculation of the velocity of any object passing both slits is a simple matter
Hubble Space Telescope Imaging of the Ultra-Compact High Velocity Cloud AGC 226067: A stripped remnant in the Virgo Cluster
We analyze the optical counterpart to the ultra-compact high velocity cloud
AGC 226067, utilizing imaging taken with the Advanced Camera for Surveys (ACS)
on the Hubble Space Telescope. The color magnitude diagram of the main body of
AGC 226067 reveals an exclusively young stellar population, with an age of
7--50 Myr, and is consistent with a metallicity of [Fe/H]0.3 as
previous work has measured via HII region spectroscopy. Additionally, the color
magnitude diagram is consistent with a distance of 17 Mpc,
suggesting an association with the Virgo cluster. A secondary stellar system
located 1.6' (8 kpc) away in projection has a similar stellar
population. The lack of an old red giant branch (5 Gyr) is contrasted
with a serendipitously discovered Virgo dwarf in the ACS field of view (Dw
J122147+132853), and the total diffuse light from AGC~226067 is consistent with
the luminosity function of the resolved 7--50 Myr stellar population. The
main body of AGC~226067 has a =11.30.3, or
=5.41.310 given the stellar population.
We searched 20 deg of imaging data adjacent to AGC~226067 in the Virgo
Cluster, and found two similar stellar systems dominated by a blue stellar
population, far from any massive galaxy counterpart -- if this population has
similar star formation properties as AGC~226067, it implies 0.1
yr in Virgo intracluster star formation. Given its unusual
stellar population, AGC~226067 is likely a stripped remnant and is plausibly
the result of compressed gas from the ram pressure stripped M86 subgroup
(350 kpc away in projection) as it falls into the Virgo Cluster.Comment: 9 pages, 4 figures, 1 table. Accepted by the Astrophysical Journa
An optical/NIR survey of globular clusters in early-type galaxies III. On the colour bimodality of GC systems
The interpretation that bimodal colour distributions of globular clusters
(GCs) reflect bimodal metallicity distributions has been challenged.
Non-linearities in the colour to metallicity conversions caused by the
horizontal branch (HB) stars may be responsible for transforming a unimodal
metallicity distribution into a bimodal (optical) colour distribution. We study
optical/near-infrared (NIR) colour distributions of the GC systems in 14 E/S0
galaxies. We test whether the bimodal feature, generally present in optical
colour distributions, remains in the optical/NIR ones. The latter colour
combination is a better metallicity proxy than the former. We use KMM and GMM
tests to quantify the probability that different colour distributions are
better described by a bimodal, as opposed to a unimodal distribution. We find
that double-peaked colour distributions are more commonly seen in optical than
in optical/NIR colours. For some of the galaxies where the optical (g-z)
distribution is clearly bimodal, the (g-K) and (z-K) distributions are better
described by a unimodal distribution. The two most cluster-rich galaxies in our
sample, NGC4486 and NGC4649, show some interesting differences. The (g-K)
distribution of NGC4649 is better described by a bimodal distribution, while
this is true for the (g-K) distribution of NGC4486 GCs only if restricted to a
brighter sub-sample with small K-band errors (< 0.05 mag). Formally, the K-band
photometric errors cannot be responsible for blurring bimodal metallicity
distributions to unimodal (g-K) colour distributions. However, simulations
including the extra scatter in the colour-colour diagrams (not fully accounted
for in the photometric errors) show that such scatter may contribute to the
disappearance of bimodality in (g-K) for the full NGC4486 sample. For the less
cluster-rich galaxies results are inconclusive due to poorer statistics.
[Abridged]Comment: A&A accepted, 15 pages, 10 figures, 4 table
The Impacat of Personality Type on Blog Participation
The objective of this study is to explore the impact of individual personality type on blog participation. Results indicate that blog participants are more likely to be introverts and perceptives
A Blue Tilt in the Globular Cluster System of the Milky Way-like Galaxy NGC 5170
Here we present HST/ACS imaging, in the B and I bands, of the edge-on Sb/Sc
galaxy NGC 5170. Excluding the central disk region region, we detect a 142
objects with colours and sizes typical of globular clusters (GCs). Our main
result is the discovery of a `blue tilt' (a mass-metallicity relation), at the
3sigma level, in the metal-poor GC subpopulation of this Milky Way like galaxy.
The tilt is consistent with that seen in massive elliptical galaxies and with
the self enrichment model of Bailin & Harris. For a linear mass-metallicity
relation, the tilt has the form Z ~ L^{0.42 +/- 0.13}. We derive a total GC
system population of 600 +/- 100, making it much richer than the Milky Way.
However when this number is normalised by the host galaxy luminosity or stellar
mass it is similar to that of M31. Finally, we report the presence of a
potential Ultra Compact Dwarf of size ~ 6 pc and luminosity M_I ~ -12.5,
assuming it is physically associated with NGC 5170.Comment: Accepted for publication in MNRAS, 11 pages, 10 figure
Identifying Very Metal-Rich Stars with Low-Resolution Spectra: Finding Planet-Search Targets
We present empirical calibrations that estimate stellar metallicity,
effective temperature and surface gravity as a function of Lick/IDS indices.
These calibrations have been derived from a training set of 261 stars for which
(1) high-precision measurements of [Fe/H], T_eff and log g have been made using
spectral-synthesis analysis of HIRES spectra, and (2) Lick indices have also
been measured. Our [Fe/H] calibration, which has precision 0.07 dex, has
identified a number of bright (V < 9) metal-rich stars which are now being
screened for hot Jupiter-type planets. Using the Yonsei-Yale stellar models, we
show that the calibrations provide distance estimates accurate to 20% for
nearby stars.
This paper outlines the second tier of the screening of planet-search targets
by the N2K Consortium, a project designed to identify the stars most likely to
harbor extrasolar planets. Discoveries by the N2K Consortium include the
transiting hot Saturn HD 149026 b (Sato et al. 2005, astro-ph/0507009) and HD
88133 b (Fischer et al. 2005). See Ammons et al. (2005, In Press) for a
description of the first tier of N2K metallicity screening, calibrations using
broadband photometry.Comment: Accepted for publication in the Astrophysical Journa
- …