440 research outputs found
Evidence for Rapid Variability in the Optical Light Curve of the Type Ia SN 2014J
We present results of high-cadence monitoring of the optical light curve of
the nearby, Type Ia SN 2014J in M82 using the 2.3m Aristarchos telescope.
and -band photometry on days 15-18 after , obtained with a
cadence of 2 min per band, reveals evidence for rapid variability at the
0.02-0.05 mag level on timescales of 15-60 min on all four nights, taking the
red noise estimation at face value. The decline slope was measured to be
steeper in the -band than in -band, and to steadily decrease in both
bands from 0.15 mag/day (night 1) to 0.04 mag/day (night 4) in V and from 0.19
mag/day (night 1) to 0.06 mag/day (night 4) in B, corresponding to the onset of
the secondary maximum. We propose that rapid variability could be due to one or
a combination of the following scenarios: the clumpiness of the ejecta, their
interaction with circumstellar material, the asymmetry of the explosion, or the
mechanism causing the secondary maximum in the near-infrared light curve. We
encourage the community to undertake high-cadence monitoring of future, nearby
and bright supernovae to investigate the intraday behavior of their light
curves.Comment: 9 pages, 6 figures, 2 tables. Accepted for publication in A&
Harmonic Analysis of Linear Fields on the Nilgeometric Cosmological Model
To analyze linear field equations on a locally homogeneous spacetime by means
of separation of variables, it is necessary to set up appropriate harmonics
according to its symmetry group. In this paper, the harmonics are presented for
a spatially compactified Bianchi II cosmological model -- the nilgeometric
model. Based on the group structure of the Bianchi II group (also known as the
Heisenberg group) and the compactified spatial topology, the irreducible
differential regular representations and the multiplicity of each irreducible
representation, as well as the explicit form of the harmonics are all
completely determined. They are also extended to vector harmonics. It is
demonstrated that the Klein-Gordon and Maxwell equations actually reduce to
systems of ODEs, with an asymptotic solution for a special case.Comment: 28 pages, no figures, revised version to appear in JM
Gauge semi-simple extension of the Poincar\'e group
Based on the gauge semi-simple tensor extension of the Poincar\'e group
another alternative approach to the cosmological term problem is proposed.Comment: Latex, 4 pages. Correction of misprint
Object-X: The Brightest Mid-IR Point Source in M33
We discuss the nature of the brightest mid-IR point source (which we dub
Object X) in the nearby galaxy M33. Although multi-wavelength data on this
object have existed in the literature for some time, it has not previously been
recognized as the most luminous mid-IR object in M33 because it is entirely
unremarkable in both optical and near-IR light. In the Local Group Galaxies
Survey, Object X is a faint red source visible in VRI and H-alpha but not U or
B. It was easily seen at JHK_s in the 2MASS survey. It is the brightest point
source in all four Spitzer IRAC bands and is also visible in the MIPS 24-micron
band. Its bolometric luminosity is 5x10^5 L_sun. The source is optically
variable on short time scales (tens of days) and is also slightly variable in
the mid-IR, indicating that it is a star. Archival photographic plates (from
1949 and 1991) show no optical source, so the star has been obscured for at
least half a century. Its properties are similar to those of the Galactic OH/IR
star IRC+10420 which has a complex dusty circumstellar structure resulting from
episodic low velocity mass ejections. We propose that Object X is a M>30 M_sun
evolved star obscured in its own dust ejected during episodic mass loss events
over at least half a century. It may emerge from its current ultra-short
evolutionary phase as a hotter post-RSG star analogous to M33 Var A. The
existence and rarity of such objects can be an important probe of a very brief
yet eventful stellar evolutionary phase.Comment: 20 pages, 10 figures. Accepted for publication by Ap
Fundamental Parameters of four Massive Eclipsing Binaries in Westerlund 1
We present fundamental parameters of 4 massive eclipsing binaries in the
young massive cluster Westerlund 1. The goal is to measure accurate masses and
radii of their component stars, which provide much needed constraints for
evolutionary models of massive stars. Accurate parameters can further be used
to determine a dynamical lower limit for the magnetar progenitor and to obtain
an independent distance to the cluster. Our results confirm and extend the
evidence for a high mass for the progenitor of the magnetar.Comment: 2 pages, to appear in the proceedings of the IAUS 282 on "From
Interacting Binaries to Exoplanets:Essential Modelling Tools" (Tatranska
Lomnica, July 18-22, 2011), Cambridge University Pres
An obscured AGN population hidden in the VIPERS galaxies: identification through spectral energy distribution decomposition
The detection of X-ray emission constitutes a reliable and efficient tool for
the selection of Active Galactic Nuclei (AGNs), although it may be biased
against the most heavily absorbed AGNs. Simple mid-IR broad-band selection
criteria identify a large number of luminous and absorbed AGNs, yet again host
contamination could lead to non-uniform and incomplete samples. Spectral Energy
Distribution (SED) decomposition is able to decouple the emission from the AGN
versus that from star-forming regions, revealing weaker AGN components. We aim
to identify the obscured AGN population in the VIPERS survey in the CFHTLS W1
field through SED modelling. We construct SEDs for 6,860 sources and identify
160 AGNs at a high confidence level using a Bayesian approach. Using optical
spectroscopy, we confirm the nature of ~85% of the AGNs. Our AGN sample is
highly complete (~92%) compared to mid-IR colour selected AGNs, including a
significant number of galaxy-dominated systems with lower luminosities. In
addition to the lack of X-ray emission (80%), the SED fitting results suggest
that the majority of the sources are obscured. We use a number of diagnostic
criteria in the optical, infrared and X-ray regime to verify these results.
Interestingly, only 35% of the most luminous mid-IR selected AGNs have X-ray
counterparts suggesting strong absorption. Our work emphasizes the importance
of using SED decomposition techniques to select a population of type II AGNs,
which may remain undetected by either X-ray or IR colour surveys.Comment: Accepted for publication in MNRAS in May 4, 2020. 18 figures, 3
tables
(In)finite extensions of algebras from their Inonu-Wigner contractions
The way to obtain massive non-relativistic states from the Poincare algebra
is twofold. First, following Inonu and Wigner the Poincare algebra has to be
contracted to the Galilean one. Second, the Galilean algebra is to be extended
to include the central mass operator. We show that the central extension might
be properly encoded in the non-relativistic contraction. In fact, any
Inonu-Wigner contraction of one algebra to another, corresponds to an infinite
tower of abelian extensions of the latter. The proposed method is
straightforward and holds for both central and non-central extensions. Apart
from the Bargmann (non-zero mass) extension of the Galilean algebra, our list
of examples includes the Weyl algebra obtained from an extension of the
contracted SO(3) algebra, the Carrollian (ultra-relativistic) contraction of
the Poincare algebra, the exotic Newton-Hooke algebra and some others. The
paper is dedicated to the memory of Laurent Houart (1967-2011).Comment: 7 pages, revtex style; v2: Minor corrections, references added; v3:
Typos correcte
Maxwell symmetries and some applications
The Maxwell algebra is the result of enlarging the Poincar\'{e} algebra by
six additional tensorial Abelian generators that make the fourmomenta
non-commutative. We present a local gauge theory based on the Maxwell algebra
with vierbein, spin connection and six additional geometric Abelian gauge
fields. We apply this geometric framework to the construction of Maxwell
gravity, which is described by the Einstein action plus a generalized
cosmological term. We mention a Friedman-Robertson-Walker cosmological
approximation to the Maxwell gravity field equations, with two scalar fields
obtained from the additional gauge fields. Finally, we outline further
developments of the Maxwell symmetries framework.Comment: 8pages. Presented at the XV-th International Conf. on 'Symmetry
Methods in Physics' (Dubna, July 2011) and at the '3rd Galileo-Xu Guangqi
meeting' (Beijing, October 2011), to appear in IJMP
The Infrared Massive Stellar Content of M83
We present an analysis of archival Spitzer images and new ground-based and
Hubble Space Telescope (HST) near-infrared (IR) and optical images of the field
of M83 with the goal of identifying rare, dusty, evolved massive stars. We
present point source catalogs consisting of 3778 objects from
Infrared Array Camera (IRAC) Band 1 (3.6 m) and Band 2 (4.5 m), and
975 objects identified in Magellan 6.5m FourStar near-IR and
images. A combined catalog of coordinate matched near- and mid-IR point sources
yields 221 objects in the field of M83. Using this photometry we identify 185
massive evolved stellar candidates based on their location in color-magnitude
and color-color diagrams. We estimate the background contamination to our
stellar candidate lists and further classify candidates based on their
appearance in Wide Field Camera 3 (WFC3) observations of M83. We find 49
strong candidates for massive stars which are very promising objects for
spectroscopic follow-up. Based on their location in a versus
diagram, we expect at least 24, or roughly 50%, to be confirmed as red
supergiants.Comment: 32 pages, 23 figures, accepted for publication in A&
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