astro-ph new abstracts, Tue, 22 Aug 00 04:00:13 GMT
0008304 — 0008328 received

astro-ph/0008304 [abs, src, ps, other] :

Title: Effects of Environment and Energy Injection on Gamma-Ray Burst
Z. G. Dai (Nanjing University)
Comments: 7 pages, To appear in the proceedings of the First KIAS International
Workshop on Astrophysics: Explosive Phenomena in Astrophysical Compact
Objects, Seoul, Korea; 24-27 May 2000

There is growing evidence that some long gamma-ray bursts (GRBs) arise from
the core collapse of massive stars, and thus it is inevitable that the
environments of these GRBs are preburst stellar winds or dense media. We
studied, for the first time, the wind model for afterglows based on the
Blandford-McKee self-similar solution of a relativistic shock, and suggested
that GRB 970616 is an interactor with a stellar wind. We also proposed a dense
medium model for some afterglows, e.g., the steepening in the light curve of
the R-band afterglow of GRB 990123 may be caused by the adiabatic shock which
has evolved from an ultrarelativistic phase to a nonrelativistic phase in a
dense medium. We further discussed the dense medium model in more details, and
investigated the effects of synchrotron self absorption and energy injection. A
shock in a dense medium becomes nonrelativistic rapidly after a short
relativistic phase. The afterglow from the shock at the nonrelativistic stage
decays more rapidly than at the relativistic stage. Since some models for GRB
energy sources predicted that a strongly magnetic millisecond pulsar may be
born during GRB formation, we discussed the effect of such a pulsar on the
evolution of the nonrelativistic shock through magnetic dipole radiation. We
found that in the pulsar energy injection case, the dense medium model fits
very well all the observational data of GRB 980519. Recently, we combined the
dense medium model with the pulsar energy injection effect to provide a good
fit to the optical afterglow data of GRB 000301C.

astro-ph/0008305 [abs, src, ps, other] :

Title: Biased Galaxy Formation And Measurements Of Beta
Andreas A. Berlind (1),
Vijay K. Narayanan (2),
David H. Weinberg (1) ((1) The Ohio State University, (2) Princeton University)
Comments: 26 pages including 9 eps figures. Submitted to ApJ

Measurements of the cosmological density parameter Omega using techniques
that exploit the gravity-induced motions of galaxies constrain, in linear
perturbation theory, the degenerate parameter combination beta = Omega^{0.6}/b,
where the linear bias parameter b is the ratio of the fluctuation amplitudes of
the galaxy and mass distributions. However, the relation between the galaxy and
mass density fields depends on the complex physics of galaxy formation, and it
can in general be non-linear, stochastic, and perhaps non-local. The
one-parameter linear bias model is almost certainly oversimplified, which leads
to the obvious question: What is the quantity beta that is actually measured by
different techniques? To address this question, we estimate beta from galaxy
distributions that are constructed by applying a variety of locally biased
galaxy formation models to cosmological N-body simulations. We compare the
values of beta estimated using three different techniques: a density-density
comparison similar to the POTENT analysis, a velocity-velocity comparison
similar to the VELMOD analysis, and an anisotropy analysis of the
redshift-space power spectrum. In most cases, we find that beta estimated using
all three methods is similar to the asymptotic value of
Omega^{0.6}/b_{sigma}(R) at large R, where b_{sigma}(R) is the ratio of rms
galaxy fluctuations to rms mass fluctuations on scale R. Thus, something close
to the conventional interpretation of beta continues to hold even for complex
bias models. Moreover, we find that beta estimates made using these three
methods should, in principle, agree with each other. It is thus unlikely that
non-linear or scale-dependent bias is responsible for the discrepancies that
exist among current measurements of beta from different techniques.

astro-ph/0008306 [abs, src, ps, other] :

Title: Can luminosity distance measurements probe the equation of state of dark
Pierre Astier
Comments: 12 pages, 3 Postscript figures, use epsfig, amssymb, amsmath.
Submitted to Physics Letters. B

Distance measurements to Type Ia supernovae (SNe Ia) at cosmological
distances indicate that the Universe is accelerating and that a large fraction
of the critical energy density exists in a component with negative pressure.
Various hypotheses on the nature of this “dark energy” can be tested via
their prediction for the equation of state of this component. If the dark
energy is due to a scalar field, its equation of state will in general vary
with time and is related to the potential of the field. We review the intrinsic
degeneracies of luminosity distance measurements and compute the expected
accuracies that can be obtained for the equation of state parameter from a
realistic high statistic SNe Ia experiment.

astro-ph/0008307 [abs, src, ps, other] :

Title: Science User Scenarios for a Virtual Observatory Design Reference
Mission: Science Requirements for Data Mining
Kirk D. Borne
Comments: 4 pages. Paper to appear in the proceedings of the June 2000 “Virtual
Observatories of the Future” conference at Caltech, edited by R. J. Brunner,
S. G. Djorgovski, & A. Szalay. (For figures and demos related to sample user
scenarios, see
this http URL .)

The knowledge discovery potential of the new large astronomical databases is
vast. When these are used in conjunction with the rich legacy data archives,
the opportunities for scientific discovery multiply rapidly. A Virtual
Observatory (VO) framework will enable transparent and efficient access,
search, retrieval, and visualization of data across multiple data repositories,
which are generally heterogeneous and distributed. Aspects of data mining that
apply to a variety of science user scenarios with a VO are reviewed. The
development of a VO should address the data mining needs of various
astronomical research constituencies. By way of example, two user scenarios are
presented which invoke applications and linkages of data across the catalog and
image domains in order to address specific astrophysics research problems.
These illustrate a subset of the desired capabilities and power of the VO, and
as such they represent potential components of a VO Design Reference Mission.

astro-ph/0008308 [abs, src, ps, other] :

Title: Structure and evolution of the inner Milky Way galaxy: results from
Jacco van Loon (IoA Cambridge, UK),
for The ISOGAL Collaboration
Comments: 4 pages, 2 figures. Oral contribution to the 1st Euroconference on
The Evolution of Galaxies. I. Observational Clues, eds. J.M. Vilchez, G.
Stasinska and E. Perez

The DENIS/ISOGAL near/mid-IR survey of the Milky Way for the first time
probes stellar populations in the innermost obscured regions of our galaxy.
Ages, metallicities and extinction-corrected luminosities are derived for these
stars individually. An old metal-rich population dominates in the inner
galactic Bulge, but there are also indications for the presence of a younger
population. The inner Bulge has a tri-axial shape, as traced by depth effects
on the observed luminosity distributions.

astro-ph/0008309 [abs, src, ps, other] :

Title: Possible direct method to determine the radius of a star from the
spectrum of gravitational wave signals
Motoyuki Saijo,
Takashi Nakamura
Comments: 4 pages with 3 eps figures, revtex.sty, accepted for publication in
Phys. Rev. Lett

We computed the spectrum of gravitational waves from a dust disk star of
radius R inspiraling into a Kerr black hole of mass M and specific angular
momentum a. We found that when R is much larger than the wave length of the
quasinormal mode, the spectrum has several peaks and the separation of peaks
$Deltaomega$ is proportional to $R^{-1}$ irrespective of M and a. This
suggests that the radius of the star in coalescing binary black hole – star
systems may be determined directly from the observed spectrum of gravitational
wave. This also suggests that the spectrum of the radiation may give us
important information in gravitational wave astronomy as in optical astronomy.

astro-ph/0008310 [abs, src, ps, other] :

Title: The M(BH)-Sigma Relation for Supermassive Black Holes
David Merritt,
Laura Ferrarese (Rutgers University)
Comments: The Astrophysical Journal, in press

We investigate the differences in the M(BH)-sigma relation derived recently
by Ferrarese & Merritt (2000) and Gebhardt et al. (2000). The shallower slope
found by the latter authors (3.75 vs. 4.8) is due partly to the use of a
regression algorithm that ignores measurement errors, and partly to the value
of the velocity dispersion adopted for a single galaxy, the Milky Way. A
steeper relation is shown to provide a better fit to black hole masses derived
from reverberation mapping studies. Combining the stellar dynamical, gas
dynamical, and reverberation mapping mass estimates, we derive a best-fit
relation M(BH) = 1.30 (+/- 0.36) X 10^8 (sigma_c/200)^{4.72(+/- 0.36)}, where
M(BH) is in solar masses, and sigma in km/s.

astro-ph/0008311 [abs, src, ps, other] :

Title: A Submillimeter Study of the Star-Forming Region NGC7129
Andreea S. Font,
George F. Mitchell,
Goeran Sandell
Comments: Submitted to ApJ

We present new molecular (13CO J=3-2 and C18O J=3-2) and dust continuum (450
and 850 micron) SCUBA observations of the NGC7129 star forming region. The maps
include the Herbig Ae/Be star LkHa 234, the far-infrared source NGC 7129 FIRS2
and several other pre-stellar sources embedded within the molecular ridge. Both
the continuum and 13CO emissions show a similar morphology, displaying a sharp
boundary towards the cavity. A new protostar (SM2) is revealed in the continuum
maps, not clearly seen in any earlier data set. Also, we are able to identify
the highest peak emission with the deeply embedded source IRS6, a few
arcseconds away from LkHa 234, and the most probable source for the molecular
outflow near LkHa 234. We make fits to the spectral energy distributions to
obtain the compact source sizes, the dust temperatures, luminosities, and
masses. A map of the 850 micron/450 micron spectral index, alpha, shows a
correlation between alpha minima and the continuum flux peaks. The dense
compact sources have dust emissivity indices, beta, of 1 to 1.6, while beta is
typically 2.0 in the surrounding cloud. The spectral index, alpha, increases
steeply from the center of the molecular ridge, through the PDR, to the
molecular cloud boundary. Although an increase in temperature will contribute
to an increase in alpha, the observed values require a rising beta through the

astro-ph/0008312 [abs, src, ps, other] :

Title: Photometric Properties of the Arp 220 Super Star Clusters
Yasuhiro Shioya,
Yoshiaki Taniguchi,
Neil Trentham
Comments: 8 pages, 5 figures. Accepted for publication in MNRAS

We investigate the photometric properties of six super stellar clusters
(SSCs) seen in both the optical and near-infrared Hubble Space Telescope images
of the local ultraluminous starburst galaxy Arp 220. Three of the SSCs are
located in the central 0.5 kpc region. The remaining three are in the
circumnuclear region between 0.5 kpc and 2.5 kpc from the centre. Comparing the
observed spectral energy distributions (SEDs) of the SSCs with the Starburst99
models of Leitherer et al., we confirm that all the three nuclear SSCs are
heavily obscured ($A_V sim 10$ mag). Considering the results from this
comparison in conjunction with measurements of the near-infrared CO absorption
index and of millimetre CO line widths and luminosities, we estimate the ages
of the nuclear SSCs to be $10^7 – 10^8$ yrs. The bolometric luminosity of the
three nuclear SSCs is at most one-fifth of the total bolometric luminosity of
Arp 220. On the other hand, the circumnuclear SSCs have little internal
extinction ($A_V leq$ 1 mag). These contribute negligibly to the total
bolometric luminosity.

astro-ph/0008313 [abs, src, ps, other] :

Title: Distribution of dust and stars in the Galaxy
Ronald Drimmel,
David Spergel
Comments: 8 pages, 4 figures, to be published in the proceedings of the 4th
Tetons Summer Conference “Galactic Structure, Stars, and the ISM,” PASP
conference series

Using far-infrared 240 micron and near-infrared K band data from the
COBE/DIRBE instrument, we model the Galactic stellar and dust distribution.
Making the assumption that the Galaxy is transparent in the 240 micron band,
the dust emission is modeled using the following components: a warped
exponential disk of scale length 0.26 R_sun, a spiral arm component as mapped
by HII regions, and a feature coinciding with the local (Orion) arm. The dust
distribution is used to calculate absorption in the K band, and the stellar
emission is likewise modeled with a warped exponential disk, with a scale
length of 0.29 R_sun, and a spiral arm component. Models of the K band emission
in the Galactic plane indicate that in this waveband a two arm spiral dominates
the nonaxisymmetric emission. The warp is evident in both the dust and stellar
component, and is found to start within the Solar Circle.

astro-ph/0008314 [abs, src, ps, other] :

Title: Opportunities for future supernova studies of cosmic acceleration
Jochen Weller,
Andreas Albrecht
Comments: Four pages including 4 figures

We investigate the potential of a future supernova dataset, as might be
obtained by the proposed SNAP satellite, to discriminate among different “dark
energy” theories that describe an accelerating Universe. We find that many
such models can be distinguished with a fit to the effective
pressure-to-density ratio, $w$, of this energy. More models can be
distinguished when the effective slope, $dw/dz$, of a changing $w$ is also fit,
but only if our knowledge of the current mass density, $Omega_m$, is improved.
We investigate the use of “fitting functions” to interpret luminosity
distance data from supernova searches, and argue in favor of a particular
preferred method, which we use in our analysis.

astro-ph/0008315 [abs, src, ps, other] :

Title: An HST Lensing Survey of X-ray Luminous Galaxy Clusters: I. A383
Graham P. Smith,
Jean-Paul Kneib,
Harald Ebeling,
Oliver Czoske,
Ian Smail
Comments: 9 pages, 8 figures (2 GIFs), submitted to ApJ

We analyse the mass distribution in the core of A383 (z=0.188), one of 12
X-ray luminous clusters at z~0.2 selected for a comprehensive and unbiased
study of the mass distribution in massive clusters. Deep HST imaging reveals a
wide variety of gravitationally lensed features in A383, including a giant arc
formed from the strongly-lensed images of 2 background galaxies, 2 radial arcs,
several multiply-imaged arcs and numerous arclets. Based upon the constraints
from the various lensed features, we construct a detailed mass model for the
central regions of the cluster, taking into account both the cluster-scale
potential and perturbations from individual cluster galaxies. Keck spectroscopy
of one component of the giant arc identifies it as a star-forming galaxy at
z=1.01 and provides an accurate measurement of the cluster mass within the
radius of the giant arc (65kpc) of (3.5+/-0.1)*10^13 Mo. Using the weak shear
measured from our HST observations we extend our mass model to determine a mass
of (1.8+/-0.2)*10^14 Mo within a radius of 250kpc. On smaller scales we employ
the radial arcs as probes of the shape of the mass distribution in the cluster
core (r<20kpc), and find that the mass profile is more peaked than a single NFW
profile. The optical and X-ray properties of A383 indicate the presence of a
central cooling flow, for which we derive a mass deposition rate of >200 Mo/yr.
We also use the X-ray emission from A383 to obtain independent estimates of the
total mass within projected radii of 65 and 250kpc: (4.0+/-1.4)*10^13 Mo and
(1.2+/-0.5)*10^14 Mo, which are consistent with the lensing measurements.

astro-ph/0008316 [abs, src, ps, other] :

Title: ISO-SWS calibration and the accurate modelling of cool-star atmospheres:
I. Method
L. Decin (1),
C. Waelkens (1),
K. Eriksson (2),
B. Gustafsson (2)
B.Plez (3),
A.J. Sauval (4),
W. Van Assche (5),
B. Vandenbussche (1) ((1) Instituut voor Sterrenkunde, Leuven, Belgium (2) Astronomiska Observatoriet, Uppsala, Sweden (3) Universite de Montpellier II, Montpellier, France (4) Observatoire Royal de Belgique, Bruxelles, Belgium (5) Instituut voor Wiskunde, Leuven, Belgium)
Comments: 20 pages, 7 figures, accepted by A&A Main Journal on August, 3 2000

A detailed spectroscopic study of the ISO-SWS data of the red giant Alpha Tau
is presented, which enables not only the accurate determination of the stellar
parameters of Alpha Tau, but also serves as a critical review of the ISO-SWS

This study is situated in a broader context of an iterative process in which
both accurate observations of stellar templates and cool star atmosphere models
are involved to improve the ISO-SWS calibration process as well as the
theoretical modelling of stellar atmospheres. Therefore a sample of cool stars,
covering the whole A0 — M8 spectral classification, has been observed in order
to disentangle calibration problems and problems in generating the theoretical
models and corresponding synthetic spectrum.

By using stellar parameters found in the literature large discrepancies were
seen between the ISO-SWS data and the generated synthetic spectrum of Alpha
Tau. A study of the influence of various stellar parameters on the theoretical
models and synthetic spectra, in conjunction with the Kolmogorov-Smirnov test
to evaluate objectively the goodness-of-fit, enables us to pin down the stellar
parameters with a high accuracy: Teff = 3850 +/- 70 K, log g = 1.50 +/- 0.15, M
= 2.3 +/- 0.8 Msun, z = -0.15 +/- 0.20 dex, microturbulence = 1.7 +/- 0.3 km/s,
12C/13C= 10 +/- 1, abundance of C = 8.35 +/- 0.20 dex, abundance of N= 8.35 +/-
0.25 dex, abundance of O = 8.83 +/- 0.15 dex and the angular diameter is 20.77
+/- 0.83 mas. These atmospheric parameters were then compared with the results
provided by other authors using other methods and/or spectra.

astro-ph/0008317 [abs, src, ps, other] :

Title: NGC1614: A Laboratory for Starburst Evolution
A. Alonso-Herrero (1,2),
C. W. Engelbracht (1),
M. J. Rieke (1),
G. H. Rieke (1),
A. C. Quillen (1) ((1) Steward Observatory (2) University of Hertfordshire)
Comments: Accepted for publication in ApJ. 20 pages (uses emulateapj)

The modest extinction and reasonably face-on viewing geometry make the
luminous IR galaxy NGC1614 an ideal laboratory for study of a powerful
starburst. HST/NICMOS observations show: 1.) deep CO stellar absorption,
tracing a starburst nucleus about 45 pc in diameter; 2.) surrounded by a ~600
pc diameter ring of supergiant HII regions revealed in Pa$alpha$ line
emission; 3.) lying within a molecular ring indicated by its extinction shadow
in H-K; 4.) all at the center of a disturbed spiral galaxy. The luminosities of
the giant HII regions in the ring are extremely high, an order of magnitude
brighter than 30 Doradus. The relation of deep stellar CO bands to surrounding
ionized gas ring to molecular gas indicates that the luminous starburst started
in the nucleus and is propagating outward into the surrounding molecular ring.
This hypothesis is supported by evolutionary starburst modeling that shows that
the properties of NGC1614 can be fitted with two short-lived bursts of star
formation separated by 5 Myr. The total dynamical mass of the starburst region
of 1.3×10^9 Msol is mostly accounted for by the old pre-star burst stellar
population. Although our starburst models use a modified Salpeter IMF, the
tight mass budget suggests that the IMF may contain relatively more 10-30 Msol
stars and fewer low mass stars than the Salpeter function. The dynamical mass
is nearly 4 times smaller than the mass of molecular gas estimated from the
standard ratio of 12CO(1-0) to H2. A number of arguments place the mass of gas
in the starburst region at ~25% of the dynamical mass, nominally about 1/15 and
with an upper limit of 1/10 of the amount estimated from 12CO and the standard
ratio. (Abridged)

astro-ph/0008318 [abs, src, ps, other] :

Title: The WIMP annual modulation signal and non-standard halo models
Anne M. Green
Comments: 6 pages, 6 .ps figures

Currently the best prospect for detecting Weakly Interacting Massive
Particles (WIMPs) is via the annual modulation, which occurs due to the Earth’s
rotation around the Sun, of the direct detection signal. We investigate the
effect of uncertainties in our knowledge of the structure of the galactic halo
on the WIMP annual modulation signal. We evaluate the signal for three
non-standard halo models: Evans’ power-law halos, Michie models with an
asymmetric velocity distribution and Maxwellian halos with bulk rotation. We
then compare the theoretical predictions of these models with the experimental
signal found by the DAMA experiment and investigate how the WIMP mass and
interaction cross section determined depend on the halo model assumed. We find
that the WIMP mass confidence limits are significantly extended to larger
masses, with the shape of the allowed region in the mass-cross section plane
depending on the model.

astro-ph/0008319 [abs, src, ps, other] :

Title: Bimodal Accretion Disks: SSD-ADAF Transitions
Wei-Min Gu,
Ju-Fu Lu
Comments: 12 pages, 3 figures, accepted by ApJ Letter

We show that, unlike the results presented previously in the literature, the
transition from an outer Shakura-Sunyaev disk (SSD) to an advection-dominated
accretion flow (ADAF) is possible for large values of the viscosity parameter
$alpha >0.5$. The transition is triggered by thermal instability of a
radiation-pressure-supported SSD. The transition radius is close to the central
black hole. We confirm our qualitative prediction by actually constructing
global bimodal SSD-ADAF solutions.

astro-ph/0008320 [abs, src, ps, other] :

Title: Comparing Giant Molecular Clouds in M31, M33 & the Milky Way
Kartik Sheth,
Stuart N. Vogel (U. Maryland),
Christine D. Wilson (McMaster University),
T. M. Dame (Harvard-Smithsonian CfA)
Comments: 4 pages including 4 figures, to be published in “The Interstellar
Medium in M31 and M33”, Proceedings 232. WE-Heraeus-Seminar held from May
22-25, 2000 in Bad Honnef in Germany

We present new observations of a 2′ field in the north-eastern spiral arm of
M31. In the 0.8 x 3.6 kpc mosaicked region, we have detected six distinct,
large complexes of molecular gas, most of which lie along the spiral arm dust
lane or in the vicinity of HII regions. The mean properties of these complexes
are as follows: diameter ~ 57+/-13 pc, fwhm velocity ~ 6.5+/-1.2 km/s, M(CO) ~
3.0+/-1.6 x 10^5 solar masses, peak brightness temperatures ~ 1.6–4.2 K. We
investigate the effects of spatial filtering on the quantitative comparison of
Local Group and Milky Way giant molecular clouds properties and distributions.
We also discuss different cloud identification techniques and their impact on
derived cloud properties. When we employ the same cloud identification method
and account for differences in data acquisition for M31, Milky Way, and M33, we
find that the molecular cloud complexes in all three galaxies are similar.
While the global distribution of molecular gas may vary from galaxy to galaxy,
cloud complexes are similar, suggesting that cloud formation and destruction is
determined by local physics. This work is supported by grants AST-9613716 &
AST-9981289 from the National Science Foundation.

astro-ph/0008321 [abs, src, ps, other] :

Title: 85-GHz BIMA observations of the double-hotspot radio galaxy 3C20
M. J. Hardcastle,
L. W. Looney
Comments: 10 pages, 8 figures, accepted by MNRAS

We present 85-GHz observations of the archetypal double-hotspot radio source
3C20 made with the BIMA millimetre array. The resolution of BIMA allows us to
separate the two components of the eastern hotspot. By comparing the BIMA
observations with existing VLA data, we show that the spectra of the two
hotspot components are very similar, despite the clear differences in their
radio structure and their wide separation. We discuss the implications for
models of double hotspot formation. Weak emission from the lobes of 3C20 is
detected at 85 GHz, at a level consistent with the predictions of standard
spectral ageing models.

astro-ph/0008322 [abs, src, ps, other] :

Title: The SPIFFI image slicer: Revival of image slicing with plane mirrors
Matthias Tecza,
Niranjan Thatte,
Frank Eisenhauer,
Sabine Mengel,
Claudia Roehrle,
Klaus Bickert
Comments: 7 pages, 4 figures, to appear in SPIE proceedings ‘Astronomical
Telescopes and Instrumentation 2000’

SPIFFI (SPectrometer for Infrared Faint Field Imaging) is the integral field
spectrograph of the VLT-instrument SINFONI (SINgle Far Object Near-infrared
Investigation). SINFONI is the combination of SPIFFI with the ESO adaptive
optics system MACAO (Multiple Application Concept for Adaptive Optics) offering
for the first time adaptive optics assisted near infrared integral field
spectroscopy at an 8m-telescope. SPIFFI works in the wavelength ranger from 1.1
to 2.5 micron with a spectral resolving power ranging from R=2000 to 4500.
Pixel scale ranges from 0.25 to 0.025 seconds of arc. The SPIFFI field-of-view
consists of 32×32 pixels which are rearranged with an image slicer to a form a
long slit. Based on the 3D slicer concept with plane mirrors, an enhanced image
slicer was developed. The SPIFFI image slicer consists of two sets of mirrors,
called the ‘small’ and the ‘large’ slicer. The small slicer cuts a square field
of view into 32 slitlets, each of which is 32 pixels long. The large slicer
rearranges the 32 slitlets into a 1024 pixels long slit. The modifications to
the 3D slicer concept affect the angles of the plane mirrors of small and large
slicer and lead to an improved slit geometry with very little light losses. At
a mirror width of 0.3mm the light loss is <5%. All reflective surfaces are flat
and can be manufactured with a high surface quality. This is especially
important for the adaptive optics mode of SINFONI. We explain the concept of
the SPIFFI mirror slicer and describe details of the manufacturing process.

astro-ph/0008323 [abs, src, ps, other] :

Title: A Newly Discovered SU UMa-Type Dwarf Nova, HS 1449+6415
D. Nogami,
D. Engels,
B. T. Gaensicke,
E. P. Pavlenko,
R. Novak,
K. Reinsch
Comments: 5 pages, 6 figures, submitted to A&A

We report time-resolved photometric observations of the Hamburg Quasar
Survey-selected dwarf nova HS 1449+6415 (= RX J1450.5+6403) during the interval
from JD 2451672 to 2451724. During a long outburst with a duration of ~12 days,
we detected superhumps with a period of 0.0601(5) d, revealing that this star
is an SU UMa star. A short outburst which lasted 3 days was found about 40 days
after the onset of the superoutburst. From quiescence observations, we
determine an orbital period of 0.05898(2) d. The small outburst amplitude of
~3.5 mag, the short orbital period, and the normal outburst cycle length
suggest that HS 1449+6415 is an intermediate object between ER UMa stars with
high mass-transfer rates and WZ Sge stars with very low mass-transfer rates.

astro-ph/0008324 [abs, src, ps, other] :

Title: HST Optical-NIR Colors of Nearby $R^{1/4}$ and Exponential Bulges
C.M. Carollo,
M. Stiavelli,
P.T. de Zeeuw,
M. Seigar,
H. Dejonghe
Comments: ApJ, accepted, Dec 10, 2000 Issue

We have analysed $V$, $H$ and $J$ HST images for a sample of early- to
late-type spiral galaxies, and reported elsewhere the statistical frequency of
$R^{1/4}$-law and exponential bulges in our sample as a function of Hubble
type, and the frequency of occurrence and structural properties of the resolved
central nuclei hosted by intermediate- to late-type bulges and disks (see
references in the text). Here we use these data to show that: {it (i)} The
$V-H$ color distribution of the $R^{1/4}$ bulges peaks around $<V-H> sim 1.3$,
with a sigma $Delta (V-H) sim 0.1$ magnitudes. Assuming a solar metallicity,
these values correspond to stellar ages of $approx 6 pm 3$ Gyrs. In contrast,
the $V-H$ color distribution of the exponential bulges peaks at $<V-H> sim
0.9$ and has a sigma $Delta (V-H) sim 0.4$ mags. This likely implies
significantly smaller ages and/or lower metallicities for (a significant
fraction of the stars in) the exponential bulges compared to the $R^{1/4}$-law
spheroids. {it (ii)} Most of the central nuclei hosted by the exponential
bulges have $V-H$ and $J-H$ colors which are compatible with relatively
unobscured stellar populations. Assuming no or little dust effects, ages $gta
1$ Gyrs are suggested for these nuclei, which in turn imply masses of about a
few 10$^6$ to a few 10$^7$ M$_odot$, i.e., sufficient to dissolve progenitor
bars with masses consistent with those inferred for the exponential bulges by
their luminosities. {it (iii)} While different bulge-nucleus pairs cover a
large range of $V-H$ colors, each bulge-nucleus pair has quite similar $V-H$
colors, and thus possibly similar stellar populations. (abridged)

astro-ph/0008325 [abs, src, ps, other] :

Title: Response of circumnuclear water masers to luminosity changes in an
active galactic nucleus
David A. Neufeld
Comments: 12 pages (AASTeX), including 4 figures. Accepted for publication in
ApJ Letters

Circumnuclear water masers can respond in two ways to changes in the
luminosity of an active galactic nucleus. First, an increase in the X-ray
luminosity can lead to an increase in the maser emissivity; and second, an
increase in the intrinsic bolometric luminosity may result in a temporary
decrease in the difference between the gas and dust temperature and a
consequent decrease in the maser output. Whilst the latter effect can occur
over a period shorter than the thermal timescale, the former effect cannot.
Quantitative estimates of the response of the water maser emissivity to changes
in either the X-ray or bolometric luminosity are presented, together with
estimates of the relevant timescales. Either mechanism could account for recent
observations by Gallimore et al. which suggest that the water maser variability
in two widely separated regions of the circumnuclear gas in NGC 1068 have been
coordinated by a signal from the active nucleus. For either mechanism, a
minimum H2 density ~ 1.E+8 cm-3 is needed to explain the observed variability

astro-ph/0008326 [abs, src, ps, other] :

Title: New VLBI Constraints for 0957+561 Lens Models
Deborah Haarsma (Calvin College),
Joseph Leh’ar (Harvard-Smithsonian Center for Astrophysics),
Rennan Barkana (Princeton Institute for Advanced Study)
Comments: 3 pages, 3 figures. The first two pages will appear in “Gravitational
Lensing: Recent Progress and Future Goals”, held July 26-30, 1999, ed. T. G.
Brainerd and C. S. Kochanek (ASP San Francisco), in press. The third page is
additional material presented at the conference which did not fit in the page
limit of the proceedings

Time-delay measurements of 0957+561 based on radio monitoring now agree with
optical monitoring. Recent models incorporate many recent observations, but the
systematic uncertainties in the models still dominate the uncertainty in the
cosmological results. VLBI observations of the milli-arcsec jet structure have
provided the most important set of modeling constraints. We present new
observations of this structure, made at 18 cm with the Very Long Baseline
Array, the Very Large Array, and the Green Bank 140 ft. telescope. Compared to
the data set of Garrett et al. (1994), ours has a similar theoretical noise
level (20 microJy), but nearly twice as many baselines (66 compared to 36) and
more uniform coverage of the UV plane. Our initial maps confirm the basic jet
structures seen by Garrett et al., with comparable RMS noise (60-80 microJy),
and are in reasonable agreement with the jet structure model of Barkana et al.
(1999). The maps also hint at a new compact component leaving the core, and a
previously undetected diffuse component at the end of the jet. Further
refinements in fringe-fitting, mapping, and self-calibration should yield
significantly lower RMS noise (closer to the theoretical level). We will use a
modified form of the CalTech VLBI Modelfit program (written by Barkana et al.
1999) to determine the magnification matrix between the images. The refined
magnification matrix should provide stronger constraints on the lens model, and
thus reduce the uncertainty in the cosmological results.

astro-ph/0008327 [abs, src, ps, other] :

Title: What is the behavior of the ISM in the SMC?
S. Stanimirovic
Comments: 4 pages, 2 figures, to appear in the proceedings of “The Evolution of
Galaxies: I Observational Clues”, eds. J.M. Vilchez, G. Stasinska & E. Perez

We describe quantitatively the neutral hydrogen (HI) and dust content of the
interstellar medium (ISM) in the Small Magellanic Cloud (SMC), using the
spatial power spectrum. The velocity modification of the HI density power
spectrum is investigated and discussed.

astro-ph/0008328 [abs, src, ps, other] :

Title: A Deep Multicolor Survey. VI. Near-Infrared Observations, Selection
Effects, and Number Counts
Paul Martini (Ohio State University)
Comments: Submitted to AJ. 28 pages, 7 embedded ps figures, AASTEX5. Also
available at this http URL

I present near-infrared J (1.25um), H (1.65um), and K (2.2um) imaging
observations of 185 square arcminutes in 21 high galactic latitude fields.
These observations reach limiting magnitudes of J ~ 21 mag, H ~ 20 mag and K ~
18.5 mag. The detection efficiency, photometric accuracy and selection biases
as a function of integrated object brightness, size, and profile shape are
quantified in detail. I evaluate several popular methods for measuring the
integrated light of faint galaxies and show that only aperture magnitudes
provide an unbiased measure of the integrated light that is independent of
apparent magnitude. These J, H, and K counts and near-infrared colors are in
best agreement with passive galaxy formation models with at most a small amount
of merging (for Omega_M = 0.3, Omega_Lambda = 0.7).


gr-qc/0008005 [abs, src, ps, other] :

Title: Baryonic and Non-Baryonic Dark Matter
Bernard Carr
Comments: To appear in Proceedings of 4th RESCUE International Symposium on
Birth and Evolution of the Universe

Cosmological nucleosynthesis calculations imply that there should be both
non-baryonic and baryonic dark matter. Recent data suggest that some of the
non-baryonic dark matter must be “hot” (i.e. massive neutrinos) and there may
also be evidence for “cold” dark matter (i.e. WIMPs). If the baryonic dark
matter resides in galactic halos, it is likely to be in the form of compact
objects (i.e. MACHOs) and these would probably be the remnants of a first
generation of pregalactic or protogalactic Population III stars. Many
candidates have been proposed – brown dwarfs, red dwarfs, white dwarfs or black
holes – and at various times each of these has been in vogue. We review the
many types of observations which can be used to constrain or exclude both
baryonic and non-baryonic dark matter candidates.

hep-ph/0008204 [abs, src, ps, other] :

Title: Grand Unification Signal from Ultra High Energy Cosmic Rays?
Z. Fodor,
S.D. Katz
Comments: 4 pages, 4 figures

The spectrum of ultra high energy (above approx 10^{18} eV) cosmic rays is
consistent with the decay of GUT scale particles. The predicted mass is
m_X=10^b GeV, where b=15.2_{-1.0}^{+1.5}.

hep-ph/0008208 [abs, src, ps, other] :

Title: Crystalline Color Superconductivity
Mark Alford (MIT),
Jeffrey Bowers (MIT),
Krishna Rajagopal (MIT)
Comments: 37 pages, LaTeX with eps figs
Subj-class: High Energy Physics – Phenomenology; Superconductivity

In any context in which color superconductivity arises in nature, it is
likely to involve pairing between species of quarks with differing chemical
potentials. For suitable values of the differences between chemical potentials,
Cooper pairs with nonzero total momentum are favored, as was first realized by
Larkin, Ovchinnikov, Fulde and Ferrell (LOFF). Condensates of this sort
spontaneously break translational and rotational invariance, leading to gaps
which vary periodically in a crystalline pattern. Unlike the original LOFF
state, these crystalline quark matter condensates include both spin zero and
spin one Cooper pairs. We explore the range of parameters for which crystalline
color superconductivity arises in the QCD phase diagram. If in some shell
within the quark matter core of a neutron star (or within a strange quark star)
the quark number densities are such that crystalline color superconductivity
arises, rotational vortices may be pinned in this shell, making it a locus for
glitch phenomena.


astro-ph/0002377 [abs, src, ps, other] :

Title: Quantum corrections to the ground state energy of inhomogeneous neutron
Aurel Bulgac,
Piotr Magierski
Comments: 10 pages, 13 figures (6 color)
Note: replaced with revised version Mon, 21 Aug 2000 22:28:08 GMT (254kb)

astro-ph/0005001 [abs, src, ps, other] :

Title: Constraints on dark matter physics from dwarf galaxies through galaxy
cluster haloes
C. Firmani (1,2),
E. D’Onghia (3),
G. Chincarini (1,4),
X. Hernandez (5),
V. Avila-Reese (2) ((1) O. di Brera, (2) UNAM, (3) U. Milano, (4) U. Milano-Bicocca, (5) O. di Arcetri)
Comments: Minor corrections after referee revision, references updated. 11
pages, includes encapsulated figures. Submitted to MNRAS (March 22)
Note: replaced with revised version Fri, 18 Aug 2000 23:13:22 GMT (102kb)

astro-ph/0007423 [abs, src, ps, other] :

Title: Neutron Stars and Quantum Billiards
Aurel Bulgac,
Piotr Magierski
Comments: 11 pages, contribution to the Nobel Symposium on Quantum Chaos Y2K,
Backaskog Castle, Sweden, June 13-17, 2000
Subj-class: Astrophysics; Chaotic Dynamics
Note: replaced with revised version Mon, 21 Aug 2000 03:15:32 GMT (10kb)

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