15,782 research outputs found
Luminosity Profiles of Merger Remnants
Using published luminosity and molecular gas profiles of the late-stage
mergers NGC 3921, NGC 7252 and Arp 220, we examine the expected luminosity
profiles of the evolved merger remnants, especially in light of the massive CO
complexes that are observed in their nuclei. For NGC 3921 and NGC 7252 we
predict that the resulting luminosity profiles will be characterized by an
r^{1/4} law. In view of previous optical work on these systems, it seems likely
that they will evolve into normal ellipticals as regards their optical
properties. Due to a much higher central molecular column density, Arp 220
might not evolve such a ``seamless'' light profile. We conclude that
ultraluminous infrared mergers such as Arp 220 either evolve into ellipticals
with anomalous luminosity profiles, or do not produce many low-mass stars out
of their molecular gas complexes.Comment: Final refereed version. Note new title. 4 pages, 2 encapsulated color
figures, uses emulateapj.sty. Accepted to ApJL. Also available at
http://www.cv.nrao.edu/~jhibbard/Remnants/remnants.htm
Techniques for n-Particle Irreducible Effective Theories
In this paper we show that the skeleton diagrams in the m-Loop nPI effective
action correspond to an infinite resummation of perturbative diagrams which is
void of double counting at the m-Loop level. We also show that the variational
equations of motion produced by the n-Loop nPI effective theory are equivalent
to the Schwinger-Dyson equations, up to the order at which they are consistent
with the underlying symmetries of the original theory. We use a diagrammatic
technique to obtain the 5-Loop 5PI effective action for a scalar theory with
cubic and quartic interactions, and verify that the result satisfies these two
statements.Comment: 43 pages, 48 figures, add a paragraph in conclusions, Figs. 25,45,46
changed, typos corrected, final version to appear in PR
The Neutral Hydrogen Distribution in Merging Galaxies: Differences between Stellar and Gaseous Tidal Morphologies
We have mapped the neutral atomic gas (HI) in the three disk-disk merger
systems NGC 520, Arp 220, and Arp 299. These systems differ from the majority
of the mergers mapped in HI, in that their stellar and gaseous tidal features
do not coincide. In particular, they exhibit large stellar tidal features with
little if any accompanying neutral gas and large gas-rich tidal features with
little if any accompanying starlight. On smaller scales, there are striking
anti-correlations where the gaseous and stellar tidal features appear to cross.
We explore several possible causes for these differences, including dust
obscuration, ram pressure stripping, and ionization effects. No single
explanation can account for all of the observed differences. The fact that each
of these systems shows evidence for a starburst driven superwind expanding in
the direction of the most striking anti-correlations leads us to suggest that
the superwind is primarily responsible for the observed differences, either by
sweeping the features clear of gas via ram pressure, or by excavating a clear
sightline towards the starburst and allowing UV photons to ionize regions of
the tails.Comment: 16 pages, 5 figures, uses emulateapj.sty. To appear in the March 2000
issue of AJ. Version with full resolution figures is available via
http://www.cv.nrao.edu/~jhibbard/HIdisp/HIdisp.htm
Multiwavelength analysis of the young open cluster NGC 2362
We present a multiwavelength analysis of the young open cluster NGC 2362.
UBVRcIc CCD photometric observations, together with available data in the
Chandra data base, near infrared data from the Two Micron All Sky Survey
(2MASS), and recently published Halpha spectroscopy were used to get
information about the evolutionary stage of the cluster and the main physical
properties of its stellar content. Cluster membership is estimated for every
individual star by means of ZAMS and isochrone fitting. The cluster is
confirmed to host a richly populated pre-main sequence (PMS), and to contain a
large amount of X-ray emitting stars, which reach from the PMS members of GK
spectral type, up to the most luminous OB type main sequence (MS) members. The
PMS cluster members show no significant age spread, and the comparison to both
PMS and post-MS isochrones suggests a younger age for the more massive MS than
for lower mass PMS members. The analysis allows to asses the validity of
currently used pre-main sequence evolutionary models, and supports the
suggestion of a well defined positive correlation of the X-ray emission from
PMS stars with their bolometric luminosity. Clear differences are found on the
other hand, between the X-ray activity properties of MS and PMS cluster
members, both in the relation between X-ray luminosity and bolometric
luminosity, and in spectral properties as well.Comment: 1 gzipped file: 1 tex file with 9 pages text. 5 ps files with
figures. Submitted to Astrophysical Journa
Recommended from our members
Lignin-Based Polyurethanes from Unmodified Kraft Lignin Fractionated by Sequential Precipitation
Pre-main sequence stars in open clusters. I. The DAY-I catalogue
We present the project we are carrying out at present, the search for and
characterisation of pre-main sequence (PMS) stars among the members of Galactic
young clusters. The observations of 10 southern clusters, nine of them located
in the Carina-Sagittarius spiral arm of the Milky Way are presented. We aim at
listing candidate PMS member stars in young clusters. The catalogued stars will
serve as a basis for future spectroscopic studies of individual objects to
determine the properties of stellar formation in the last phases before the
main sequence stage. Properties such as the presence of residual envelopes or
disks, age spread among PMS members, and the possible presence of several
episodes of star formation in the clusters, are to be addressed.
Multicolour photometry in the UBVRcIc system has been obtained for 10
southern young clusters in the fourth Galactic quadrant, located between
Galactic longitudes l=238 and l=310. For six clusters in the sample, the
observations presented here provide the first published study based on CCD
photometry. A quantitative comparison is performed with post-MS isochrones, and
PMS isochrones from three different evolutionary models are used in the
photometric membership analysis for possible PMS stars. The observations
produce photometric indices in the Johnson-Cousins photometric systems for a
total of 26962 stars. Matching with the 2MASS data base provides astrometric
calibration for all stars, and JHK 2MASS indices for 60 per cent of them.
Post-MS cluster ages range from 4 to 60 Myr, whereas the photometric membership
analysis assigns PMS membership to a total of 842 stars, covering an age range
between 1 and 10 Myr. A catalogue, named DAY-I, with the information on the PMS
candidate members has been ellaborated.Comment: 15 pages, 10 figures. Accepted in Astronomy and Astrophysics:
30.1.200
Physical parameters of pre-main sequence stars in open clusters
Our aims are twofold: To determine the physical parameters of PMS members in
young open clusters (YOCs), and to check and compare the performances of
different model isochrones.
We compare UBVRI photometric observations of YOCs to theoretical isochrones
in the photometric diagrams. The comparison simultaneously provides membership
assignments for MS and PMS stars, and estimates for the masses, ages, and
spatial distribution of the candidate members.
The relations found between the different cluster parameters show that the
procedure applied to assign cluster membership, and to measure physical
parameters for the selected members, is well founded.Comment: 11 pages, 8 figures. Accepted for publication in Astronomy and
Astrophysics (17.5.2011
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