3,044 research outputs found
A photometricity and extinction monitor at the Apache Point Observatory
An unsupervised software ``robot'' that automatically and robustly reduces
and analyzes CCD observations of photometric standard stars is described. The
robot measures extinction coefficients and other photometric parameters in real
time and, more carefully, on the next day. It also reduces and analyzes data
from an all-sky camera to detect clouds; photometric data taken
during cloudy periods are automatically rejected. The robot reports its
findings back to observers and data analysts via the World-Wide Web. It can be
used to assess photometricity, and to build data on site conditions. The
robot's automated and uniform site monitoring represents a minimum standard for
any observing site with queue scheduling, a public data archive, or likely
participation in any future National Virtual Observatory.Comment: accepted for publication in A
A Deep ROSAT HRI Observation of NGC 1313
We describe a series of observations of NGC 1313 using the ROSAT HRI with a
combined exposure time of 183.5 ksec. The observations span an interval between
1992 and 1998; the purpose of observations since 1994 was to monitor the X-ray
flux of SN1978K, one of several luminous sources in the galaxy. No diffuse
emission is detected in the galaxy to a level of ~1-2x10^37 ergs/s/arcmin^-2. A
total of eight sources are detected in the summed image within the D_25
diameter of the galaxy. The luminosities of five of the eight range from
\~6x10^37 to ~6x10^38 erg/s; these sources are most likely accreting X-ray
binaries, similar to sources obseved in M31 and M33. The remaining three
sources all emit above 10^39 erg/s. We present light curves of the five
brightest sources. Variability is detected at the 99.9% level from four of
these. We identify one of the sources as an NGC 1313 counterpart of a Galactic
X-ray source. The light curve, though crudely sampled, most closely resembles
that of a Galactic black hole candidate such as GX339-4, but with considerably
higher peak X-ray luminosity. An additional seven sources lie outside of the
D_25 diameter and are either foreground stars or background AGN.Comment: 18 pages, 9 figures; accepted AJ, scheduled for November 200
Exploring the inner region of Type 1 AGNs with the Keck interferometer
The exploration of extragalactic objects with long-baseline interferometers
in the near-infrared has been very limited. Here we report successful
observations with the Keck interferometer at K-band (2.2 um) for four Type 1
AGNs, namely NGC4151, Mrk231, NGC4051, and the QSO IRAS13349+2438 at z=0.108.
For the latter three objects, these are the first long-baseline interferometric
measurements in the infrared. We detect high visibilities (V^2 ~ 0.8-0.9) for
all the four objects, including NGC4151 for which we confirm the high V^2 level
measured by Swain et al.(2003). We marginally detect a decrease of V^2 with
increasing baseline lengths for NGC4151, although over a very limited range,
where the decrease and absolute V^2 are well fitted with a ring model of radius
0.45+/-0.04 mas (0.039+/-0.003 pc). Strikingly, this matches independent radius
measurements from optical--infrared reverberations that are thought to be
probing the dust sublimation radius. We also show that the effective radius of
the other objects, obtained from the same ring model, is either roughly equal
to or slightly larger than the reverberation radius as a function of AGN
luminosity. This suggests that we are indeed partially resolving the dust
sublimation region. The ratio of the effective ring radius to the reverberation
radius might also give us an approximate probe for the radial structure of the
inner accreting material in each object. This should be scrutinized with
further observations.Comment: accepted for publication in A&A Letter
Anharmonic transitions in nearly dry L-cysteine I
Two special dynamical transitions of universal character have been recently
observed in macromolecules at K and K.
Despite their relevance, a complete understanding of the nature of these
transitions and their consequences for the bio-activity of the macromolecule is
still lacking. Our results and analysis concerning the temperature dependence
of structural, vibrational and thermodynamical properties of the orthorhombic
polymorph of the amino acid L-cysteine (at a hydration level of 3.5%) indicated
that the two referred temperatures define the triggering of very simple and
specific events that govern all the biochemical interactions of the
biomolecule: activation of rigid rotors (), phonon-phonon interactions
with phonons of water dimer (), and water rotational barriers
surpassing ().Comment: 4 pages, 4 figures, submitted to Physical Review Letter
Optical identification of hard X-ray source IGRJ18257-0707
We present the results of the optical identification of hard X-ray source
IGRJ18257-0707 trough the spectroscopic observations of its optical counterpart
with RTT150 telescope. Accurate position of the X-ray source, determined using
Chandra observations, allowed us to associate this source with the faint
optical object (m_R=~20.4), which shows broad H_\alpha emission line in its
optical spectrum. Therefore we conclude that the source IGRJ18257-0707 is a
type 1 Seyfert galaxy at redshift z=0.037.Comment: 4 pages, 3 figures, accepted for publication in Astronomy Letters,
the original text in Russian can be found at
http://hea.iki.rssi.ru/~rodion/pigrj18257-0707.pd
Shadow of a Colossus: A z=2.45 Galaxy Protocluster Detected in 3D Ly-a Forest Tomographic Mapping of the COSMOS Field
Using moderate-resolution optical spectra from 58 background Lyman-break
galaxies and quasars at within a area of the
COSMOS field ( projected area density or mean transverse separation), we reconstruct a 3D
tomographic map of the foreground Ly forest absorption at
with an effective smoothing scale of
comoving. Comparing with 61
coeval galaxies with spectroscopic redshifts in the same volume, we find that
the galaxy positions are clearly biased towards regions with enhanced IGM
absorption in the tomographic map. We find an extended IGM overdensity with
deep absorption troughs at associated with a recently-discovered
galaxy protocluster at the same redshift. Based on simulations matched to our
data, we estimate the enclosed dark matter mass within this IGM overdensity to
be , and
argue based on this mass and absorption strength that it will form at least one
galaxy cluster with , although its elongated nature suggests that
it will likely collapse into two separate clusters. We also point out a compact
overdensity of six MOSDEF galaxies at within a radius and , which does not appear
to have a large associated IGM overdensity. These results demonstrate the
potential of Ly forest tomography on larger volumes to study galaxy
properties as a function of environment, as well as revealing the large-scale
IGM overdensities associated with protoclusters and other features of
large-scale structure.Comment: To be submitted to ApJ. Figure 3 can be viewed on Youtube:
https://youtu.be/KeW1UJOPMY
A Deep Photometric Look at Two of Andromeda's Dwarf Spheroidals: X and XVII
We use deep wide-field photometry from the Large Binocular Camera to study
the stellar and structural properties of the recently discovered Andromeda X
and Andromeda XVII (And X and And XVII) dwarf galaxies. Using the mean apparent
magnitude of the horizontal branch (HB), we derive distances of 621 +- 20 kpc
to And X and 734+- 23 kpc to And XVII, closer by >60 kpc than the previous
estimates which were based on red giant branch (RGB) observations. Thus our
results warrant against the use of the RGB tip method for determining distances
to systems with sparsely populated RGBs, and show how crucial HB observations
are in obtaining accurate distances in systems such as these. We find that And
X is a relatively faint (MV = -7.36), highly elongated (e = 0.48) system at a
distance of 174 +- 62 kpc from Andromeda. And XVII is brighter (MV = -8.61)
with an M31-centric distance of 73 kpc which makes it one of the closest
satellites to Andromeda. Both galaxies are metal-poor: we derive =-2.2
for And X, while And XVII shows = -2.0, consistent with the relation
of higher luminosity dwarfs being more metal- rich. Additionally, both galaxies
show considerable intrinsic spreads in metallicity (0.2 and 0.3 dex for And X
and And XVII respectively), consistent with multiple stellar populations.Comment: 8 pages, 6 figure
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