488 research outputs found
Optical, near-IR and -ray observations of SN 2015J and its host galaxy
SN 2015J was discovered on April 27th 2015 and is classified as a type IIn
supernova. At first, it appeared to be an orphan SN candidate, i.e. without any
clear identification of its host galaxy. Here, we present the analysis of the
observations carried out {by the VLT 8-m class telescope with the FORS2 camera
in the R band and the Magellan telescope (6.5 m) equipped with the IMACS
Short-Camera (V and I filters) and the FourStar camera (Ks filter)}. We show
that SN 2015J resides in what appears to be a very compact galaxy establishing
a relation between the SN event and its natural host. We also present and
discuss archival and new -ray data centred on SN 2015J. At the time of the
supernova explosion, Swift/XRT observations were made and a weak X-ray source
was detected at the location of SN 2015J. Almost one year later, the same
source was unambiguously identified during serendipitous observations by
Swift/XRT and -Newton, clearly showing an enhancement of the 0.3-10 keV
band flux by a factor with respect to the initial state. Swift/XRT
observations show that the source is still active in the -rays at a level of
counts s. The unabsorbed X-ray luminosity derived from the
{\it XMM}-Newton slew and SWIFT observations, erg
s, places SN 2015J among the brightest young supernovae in X-rays.Comment: The Astrophysical Journal, Volume 850, Number
HP Cet and Swift J0820.6-2805: two candidate intermediate polars observed by XMM-Newton
We report on the XMM-Newton observation of HP Cet and Swift J0820.6-2805, two
X-ray photon sources that are candidates to be members of the intermediate
polar class of cataclysmic variables. If the historical optical light curve of
HP Cet shows a periodic feature at minutes, a clear identification
of such a signature in the high energy band (apart for a variability on a time
scale of minutes as detected by the ROSAT satellite) is lacking. By
using XMM-Newton archive data, we clearly identify a feature (at
minutes) which is marginally consistent with one of the binary system orbital
periods reported in the literature. We also found a signature of a periodic
features on the time scale of minutes. In the case of Swift
J0820.6-2805, the intermediate polar nature was previously unclear and the
orbital and the white dwarf spin periods were unknown. Here, the 0.3-10 keV
data undoubtedly reveal an orbital period and a white dwarf spin of minutes and minutes, respectively. The spectral analysis
showed that both HP Cet and Swift J0820.6-280 are members of the under-luminous
IP subclass since their luminosity in the keV band is estimated to be
erg s and erg
s, respectively.Comment: Accepted for publication on MNRAS, main journal, 2020. 9 Pages. 9
Figure
The infrared emission of carbonaceous particles around C-rich IRAS sources
The IRAS spectra of 23 carbon-rich sources have been fitted by means of an improved theoretical model based on the Leung-Spagna radiative transfer code and using extinction data obtained in our laboratory for different types of amorphous carbon and silicon carbide submicron particles. The agreement between observations and theoretical spectra is rather good. However, a comparison between the IRAS
spectrum of the object 1244710425 (RU Vir) and that recently obtained at UKIRT, for the same object but with higher resolution, seems to open new problems
Spitzer-IRAC survey of molecular jets in Vela-D
We present a survey of H2 jets from young protostars in the Vela-D molecular
cloud (VMR-D), based on Spitzer -IRAC data between 3.6 and 8.0 micron. Our
search has led to the identification of 15 jets and about 70 well aligned knots
within 1.2 squared degree. We compare the IRAC maps with observations of the H2
1-0 S(1) line at 2.12 micron, with a Spitzer-MIPS map at 24 and 70 micron, and
with a map of the dust continuum emission at 1.2 mm. We find a association
between molecular jets and dust peaks. The jet candidate exciting sources have
been searched for in the published catalog of the Young Stellar Objects of
VMR-D. We selected all the sources of Class II or earlier which are located
close to the jet center and aligned with it.The association between jet and
exciting source was validated by estimating the differential extinction between
the jet opposite lobes. We are able to find a best-candidate exciting source in
all but two jets. Four exciting sources are not (or very barely) observed at
wavelengths shorter than 24 micron, suggesting they are very young protostars.
Three of them are also associated with the most compact jets. The exciting
source Spectral Energy Distributions have been modeled by means of the
photometric data between 1.2 micron and 1.2 mm. From SEDs fits we derive the
main source parameters, which indicate that most of them are low-mass
protostars. A significant correlation is found between the projected jet length
and the [24] - [70] color, which is consistent with an evolutionary scenario
according to which shorter jets are associated with younger sources. A rough
correlation is found between IRAC line cooling and exciting source bolometric
luminosity, in agreement with the previous literature. The emerging trend
suggests that mass loss and mass accretion are tightly related phenomena and
that both decrease with time.Comment: Accepted by The Astrophysical Journa
cynara cardunculus and coffee grounds as promising biodiesel sources for internal combustion compression ignition engines
Abstract In this study, the effect of using two innovative biodiesels - derived respectively from coffee grounds and Cynara cardunculus - in blend with neat diesel fuel, on combustion and emissions in a compression ignition engine has been investigated. During tests, load and exhaust gas recirculation were varied and results compared with those obtained with neat diesel fuel and its blends with Brassica carinata or waste cooking oil derived biodiesels. Results show a reduction or a comparable NOx and CO emission levels using Cynara cardunculus and coffee ground compared to the other fuels tested, while PM and THC emissions are penalized. Fuel consumption, as expected, is slightly reduced. EGR reduces NOx levels, while CO, THC and PM are generally penalized
Measuring polarization in microlensing events
We reconsider the polarization of the star light that may arise during microlensing events due to the high gradient of magnification across the atmosphere of the source star, by exploring the full range of microlensing and stellar physical parameters. Since it is already known that only cool evolved giant stars give rise to the highest polarization signals, we follow the model by Simmons etal. to compute the polarization as due to the photon scattering on dust grains in the stellar wind. Motivated by the possibility to perform a polarization measurement during an ongoing microlensing event, we consider the recently reported event catalogue by the Optical Gravitational Lensing Experiment (OGLE) collaboration covering the 2001-2009 campaigns (OGLE-III events), that makes available the largest and more comprehensive set of single-lens microlensing events towards the Galactic bulge. The study of these events, integrated by a Monte Carlo analysis, allows us to estimate the expected polarization profiles and to predict for which source stars and at which time is most convenient to perform a polarization measurement in an ongoing event. We find that about two dozens of OGLE-III events (about 1 per cent of the total) have maximum polarization degree in the range 0.1<Pmax<1 per cent, corresponding to source stars with apparent magnitude I≲14.5, being very cool red giants. This signal is measurable by using the FOcal Reducer and low dispersion Spectrograph (FORS2) polarimeter at Very Large Telescope (VLT) telescope with about 1h integration tim
Measuring Polarization in microlensing events
We re-consider the polarization of the star light that may arise during
microlensing events due to the high gradient of magnification across the
atmosphere of the source star, by exploring the full range of microlensing and
stellar physical parameters. Since it is already known that only cool evolved
giant stars give rise to the highest polarization signals, we follow the model
by Simmons et al. (2002) to compute the polarization as due to the photon
scattering on dust grains in the stellar wind. Motivated by the possibility to
perform a polarization measurement during an ongoing microlensing event, we
consider the recently reported event catalog by the OGLE collaboration covering
the 2001-2009 campaigns (OGLE-III events), that makes available the largest and
more comprehensive set of single lens microlensing events towards the Galactic
bulge. The study of these events, integrated by a Monte Carlo analysis, allows
us to estimate the expected polarization profiles and to predict for which
source stars and at which time is most convenient to perform a polarization
measurement in an ongoing event. We find that about two dozens of OGLE-III
events (about 1 percent of the total) have maximum polarization degree in the
range 0.1 < P_{\rm max} <1 percent, corresponding to source stars with apparent
magnitude I < 14.5, being very cool red giants.This signal is measurable by
using the FORS2 polarimeter at VLT telescope with about 1 hour integration
time.Comment: Originally submitted to MNRAS on 01/07/2014. Present version with
minor changes as required by the Refere
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