31 research outputs found
Reviews
Review of Jurisdiction under the Industrial Relations Act 1973: Some Problems and Issues, Employment: Towards an Active Employment Policy, Labor in the American Economy, Strikes and Participation, Democracy in the Work Place
Activity of 50 Long-Period Comets Beyond 5.2 AU
Remote investigations of the ancient solar system matter has been
traditionally carried out through the observations of long-period (LP) comets
that are less affected by solar irradiation than the short-period counterparts
orbiting much closer to the Sun. Here we summarize the results of our
decade-long survey of the distant activity of LP comets. We found that the most
important separation in the dataset is based on the dynamical nature of the
objects. Dynamically new comets are characterized by a higher level of activity
on average: the most active new comets in our sample can be characterized by
afrho values >3--4 higher than that of our most active returning comets. New
comets develop more symmetric comae, suggesting a generally isotropic outflow.
Contrary to this, the coma of recurrent comets can be less symmetrical,
ocassionally exhibiting negative slope parameters, suggesting sudden variations
in matter production. The morphological appearance of the observed comets is
rather diverse. A surprisingly large fraction of the comets have long, teniouos
tails, but the presence of impressive tails does not show a clear correlation
with the brightness of the comets.Comment: 21 pages, 4 figures, accepted for publication in A
Extensive Spectroscopy and Photometry of the Type IIP Supernova 2013ej
We present extensive optical (, , and open CCD) and
near-infrared () photometry for the very nearby Type IIP SN ~2013ej
extending from +1 to +461 days after shock breakout, estimated to be MJD
. Substantial time series ultraviolet and optical spectroscopy
obtained from +8 to +135 days are also presented. Considering well-observed SNe
IIP from the literature, we derive bolometric calibrations from
and unfiltered measurements that potentially reach 2\% precision with a
color-dependent correction. We observe moderately strong Si II
as early as +8 days. The photospheric velocity () is
determined by modeling the spectra in the vicinity of Fe II
whenever observed, and interpolating at photometric epochs based on a
semianalytic method. This gives km s at +50
days. We also observe spectral homogeneity of ultraviolet spectra at +10--12
days for SNe IIP, while variations are evident a week after explosion. Using
the expanding photosphere method, from combined analysis of SN 2013ej and SN
2002ap, we estimate the distance to the host galaxy to be
Mpc, consistent with distance estimates from other methods. Photometric and
spectroscopic analysis during the plateau phase, which we estimated to be
days long, yields an explosion energy of
ergs, a final pre-explosion progenitor mass of ~M and a
radius of ~R. We observe a broken exponential profile beyond
+120 days, with a break point at + days. Measurements beyond this
break time yield a Ni mass of ~M.Comment: 29 pages, 23 figures, 15 tables, Published in The Astrophisical
Journa
SN 2016coi/ASASSN-16fp: An example of residual helium in a type Ic supernova?
The optical observations of Ic-4 supernova (SN) 2016coi/ASASSN-16fp, from
to days after explosion, are presented along with analysis
of its physical properties. The SN shows the broad lines associated with SNe
Ic-3/4 but with a key difference. The early spectra display a strong absorption
feature at \AA\ which is not seen in other SNe~Ic-3/4 at this
epoch. This feature has been attributed to He I in the literature. Spectral
modelling of the SN in the early photospheric phase suggests the presence of
residual He in a C/O dominated shell. However, the behaviour of the He I lines
are unusual when compared with He-rich SNe, showing relatively low velocities
and weakening rather than strengthening over time. The SN is found to rise to
peak d after core-collapse reaching a bolometric luminosity of Lp
\ergs. Spectral models, including the nebular epoch, show
that the SN ejected \msun\ of material, with \msun\ below
5000 \kms, and with a kinetic energy of erg. The
explosion synthesised \msun\ of 56Ni. There are significant
uncertainties in E(B-V)host and the distance however, which will affect Lp and
MNi. SN 2016coi exploded in a host similar to the Large Magellanic Cloud (LMC)
and away from star-forming regions. The properties of the SN and the
host-galaxy suggest that the progenitor had of \msun\
and was stripped almost entirely down to its C/O core at explosion.Comment: Accepted for publication in MNRAS. Updated to reflect the published
version, minor typographical changes onl
An UXor among FUors: Extinction-related Brightness Variations of the Young Eruptive Star V582 Aur
V582 Aur is an FU Ori-type young eruptive star in outburst since similar to 1985. The eruption is currently in a relatively constant plateau phase, with photometric and spectroscopic variability superimposed. Here we will characterize the progenitor of the outbursting object, explore its environment, and analyze the temporal evolution of the eruption. We are particularly interested in the physical origin of the two deep photometric dips, one that occurred in 2012 and one that is ongoing since 2016. We collected archival photographic plates and carried out new optical, infrared, and millimeter-wave photometric and spectroscopic observations between 2010 and 2018, with a high sampling rate during the current minimum. Besides analyzing the color changes during fading, we compiled multiepoch spectral energy distributions and fitted them with a simple accretion disk model. Based on pre-outburst data and a millimeter continuum measurement, we suggest that the progenitor of the V582 Aur outburst is a low-mass T Tauri star with average properties. The mass of an unresolved circumstellar structure, probably a disk, is 0.04M(circle dot). The optical and near-infrared spectra demonstrate the presence of hydrogen and metallic lines, show the CO band head in absorption, and exhibit a variable Ha profile. The color variations strongly indicate that both the similar to 1 yr long brightness dip in 2012 and the current minimum since 2016 are caused by increased extinction along the line of sight. According to our accretion disk models, the reddening changed from A(V) = 4.5 to 12.5mag, while the accretion rate remained practically constant. Similarly to the models of the UXor phenomenon of intermediate- and low-mass young stars, orbiting disk structures could be responsible for the eclipses
Absolute Distances to Nearby Type Ia Supernovae via Light Curve Fitting Methods
We present a comparative study of absolute distances to a sample of very nearby, bright Type Ia supernovae (SNe) derived from high cadence, high signal-to-noise, multi-band photometric data. Our sample consists of four SNe: 2012cg, 2012ht, 2013dy and 2014J. We present new homogeneous, high-cadence photometric data in Johnson-Cousins BVRI and Sloan g' r' i' z' bands taken from two sites (Piszkesteto and Baja, Hungary), and the light curves are analyzed with publicly available light curve fitters (MLCS2k2, SNooPy2 and SALT2.4). When comparing the best-fit parameters provided by the different codes, it is found that the distance moduli of moderately reddened SNe Ia agree within less than or similar to 0.2 mag, and the agreement is even better (less than or similar to 0.1 mag) for the highest signal-to-noise BVRI data. For the highly reddened SN 2014J the dispersion of the inferred distance moduli is slightly higher. These SN-based distances are in good agreement with the Cepheid distances to their host galaxies. We conclude that the current state-of-the-art light curve fitters for Type Ia SNe can provide consistent absolute distance moduli having less than similar to 0.1-0.2 mag uncertainty for nearby SNe. Still, there is room for future improvements to reach the desired similar to 0.05 mag accuracy in the absolute distance modulus
SN 2017gmr: An Energetic Type II-P Supernova with Asymmetries
We present high-cadence UV, optical, and near-infrared data on the luminous Type II-P supernova SN2017gmr from hours after discovery through the first 180 days. SN2017gmr does not show signs of narrow, high-ionization emission lines in the early optical spectra, yet the optical light-curve evolution suggests that an extra energy source from circumstellar medium (CSM) interaction must be present for at least 2 days after explosion. Modeling of the early light curve indicates a ∼500 Re progenitor radius, consistent with a rather compact red supergiant, and latetime luminosities indicate that up to 0.130±0.026 Me of 56Ni are present, if the light curve is solely powered by radioactive decay, although the 56Ni mass may be lower if CSM interaction contributes to the post-plateau luminosity. Prominent multipeaked emission lines of Hα and [O I] emerge after day 154, as a result of either an asymmetric explosion or asymmetries in the CSM. The lack of narrow lines within the first 2 days of explosion in the likely presence of CSM interaction may be an example of close, dense, asymmetric CSM that is quickly enveloped by the spherical supernova ejecta