257 research outputs found
Outburst evolution, historic light curve and a flash-ionized nebula around the WZ Sge-type object PNV J03093063+2638031
We have monitored the 2014 superoutburst of the WZ Sge-type transient PNV
J03093063+2638031 for more than four months, from V=11.0 maximum brightness
down to V=18.4 mag, close to quiescence value, by obtaining BVRI photometry and
low resolution fluxed spectroscopy. The evolution was normal and no late-time
`echo' outbursts were observed. The absolute integrated flux of emission lines
kept declining along the superoutburst, and their increasing contrast with the
underlying continuum was simply the result of the faster decline of the
continuum compared to the emission lines. Inspection of historical Harvard
plates covering the 1899-1981 period did not reveal previous outbursts, neither
`normal' nor 'super'. We discovered an extended emission nebula (radius ~1
arcmin) around PNV J03093063+2638031, that became visible for a few months as
the result of photo-ionization from the superoutburst of the central star. It
is not present on Palomar I and II sky survey images and it quickly disappeared
when the outburst was over. From the rate at wich the inization front swept
through the nebula, we derive a distance of ~120 pc to the system. The nebula
is density bounded with an outer radius of 0.03 pc, and the absolute magnitude
of the central star in quiescence is M(V)~14.2 mag. The electron density in the
nebula is estimated to be 10(+5) cm(-3) from the observed recombination time
scale. Given the considerable substructures seen across the nebula, a low
filling factor is inferred. Similar nebulae have not been reported for other WZ
Sge objects and the challenges posed to models are considered.Comment: Astronomy & Astrophysic
Variable stars in one open cluster within the Kepler/K2-Campaign-5 field: M 67 (NGC 2682)
In this paper we continue the release of high-level data products from the
multiyear photometric survey collected at the 67/92 cm Schmidt Telescope in
Asiago. The primary goal of the survey is to discover and to characterise
variable objects and exoplanetary transits in four fields containing five
nearby open clusters spanning a broad range of ages. This second paper releases
a photometric catalogue, in five photometric bands, of the Solar-age,
Solar-metallicity open cluster M 67 (NGC 2682). Proper motions are derived
comparing the positions observed in 2013 at the Asiago's Schmidt Telescope with
those extracted from [email protected] MPG/ESO images in 2000. We also analyse the
variable sources within M 67. We detected 68 variables, 43 of which are new
detection. Variable periods and proper-motion memberships of a large majority
of sources in our catalogue are improved with respect to previous releases. The
entire catalogue will be available in electronic format. Besides the general
interest on an improved catalogue, this work will be particularly useful
because of: (1) the imminent release of Kepler/K2 Campaign-5 data of this
cluster, for which our catalogue will provide an excellent, high spatial
resolution input list, and (2) characterisation of the M 67 stars which are
targets of intense HARPS and HARPS-N radial-velocity surveys for planet search.Comment: 8 pages, 6 figures (2 at low resolution), 2 tables. Accepted for
publication in MNRAS on October 17, 2015. Electronic materials available at
the url http://groups.dfa.unipd.it/ESPG/M67.html , and later on the Journal
and at the CD
Interstellar Comet 2I/Borisov exhibits a structure similar to native Solar System comets
We processed images taken with the Hubble Space Telescope (HST) to
investigate any morphological features in the inner coma suggestive of a
peculiar activity on the nucleus of the interstellar comet 2I/Borisov. The coma
shows an evident elongation, in the position angle (PA) ~0-180d direction,
which appears related to the presence of a jet originating from a single active
source on the nucleus. A counterpart of this jet directed towards PA ~10d was
detected through analysis of the changes of the inner coma morphology on HST
images taken in different dates and processed with different filters. These
findings indicate that the nucleus is probably rotating with a spin axis
projected near the plane of the sky and oriented at PA ~100d-280d, and that the
active source is lying in a near-equatorial position. Subsequent observations
of HST allowed us to determine the direction of the spin axis at
RA=17h20m+/-15d and Dec = -35d+\-10d.Comment: 5 pages, 6 figures (low resolution). Full-resolution figures and
bonus material at this url
https://web.oapd.inaf.it/bedin/files/PAPERs_eMATERIALs/BORISOV_comet/
Accepted for publication in MNRAS Letters on 2020 April 1st (not a joke ;
The two Ultraluminous X-ray sources in the galaxy NGC 925
NGC 925 ULX-1 and ULX-2 are two ultraluminous X-ray sources in the galaxy NGC
925, at a distance of 8.5 Mpc. For the first time, we analyzed high quality,
simultaneous XMM-Newton and NuSTAR data of both sources. Although at a first
glance ULX-1 resembles an intermediate mass black hole candidate (IMBH) because
of its high X-ray luminosity ( erg s) and its
spectral/temporal features, a closer inspection shows that its properties are
more similar to those of a typical super-Eddington accreting stellar black hole
and we classify it as a `broadened disc' ultraluminous X-ray source. Based on
the physical interpretation of this spectral state, we suggest that ULX-1 is
seen at small inclination angles, possibly through the evacuated cone of a
powerful wind originating in the accretion disc. The spectral classification of
ULX-2 is less certain, but we disfavour an IMBH accreting at sub-Eddington
rates as none of its spectral/temporal properties can be associated to either
the soft or hard state of Galactic accreting black hole binaries.Comment: Accepted on MNRAS with very minor comments, 7 pages, 5 figures, 1
tabl
The nature and evolution of Nova Cygni 2006
AIMS: Nova Cyg 2006 has been intensively observed throughout its full
outburst. We investigate the energetics and evolution of the central source and
of the expanding ejecta, their chemical abundances and ionization structure,
and the formation of dust. METHOD: We recorded low, medium, and/or
high-resolution spectra (calibrated into accurate absolute fluxes) on 39
nights, along with 2353 photometric UBVRcIc measures on 313 nights, and
complemented them with IR data from the literature. RESULTS: The nova displayed
initially the normal photometric and spectroscopic evolution of a fast nova of
the FeII-type. Pre-maximum, principal, diffuse-enhanced, and Orion absorption
systems developed in a normal way. After the initial outburst, the nova
progressively slowed its fading pace until the decline reversed and a second
maximum was reached (eight months later), accompanied by large spectroscopic
changes. Following the rapid decline from second maximum, the nova finally
entered the nebular phase and formed optically thin dust. We computed the
amount of formed dust and performed a photo-ionization analysis of the
emission-line spectrum during the nebular phase, which showed a strong
enrichment of the ejecta in nitrogen and oxygen, and none in neon, in agreement
with theoretical predictions for the estimated 1.0 Msun white dwarf in Nova Cyg
2006. The similarities with the poorly investigated V1493 Nova Aql 1999a are
discussed.Comment: in press in Astronomy and Astrophysic
SN 2013df, a double-peaked IIb supernova from a compact progenitor and an extended H envelope
Optical observations of the type IIb SN 2013df from a few days to about 250
days after explosion are presented. These observations are complemented with UV
photometry taken by \textit{SWIFT} up to 60 days post-explosion. The
double-peak optical light curve is similar to those of SNe 1993J and 2011fu
although with different decline and rise rates. From the modelling of the
bolometric light curve, we have estimated that the total mass of synthesised
Ni in the explosion is M, while the ejecta mass is
M and the explosion energy erg. In
addition, we have estimated a lower limit to the progenitor radius ranging from
. The spectral evolution indicates that SN 2013df had a
hydrogen envelope similar to SN 1993J ( M). The line
profiles in nebular spectra suggest that the explosion was asymmetric with the
presence of clumps in the ejecta, while the [O\,{\sc i}]
, luminosities, may indicate that the progenitor
of SN 2013df was a relatively low mass star ( M).Comment: 18 pages, 11 figures, 9 tables, accepted for publication in MNRA
The variable carbon star CGCS 6107
The spectroscopic and photometric variability of CGCS 6107 has been studied with four telescopes from 2015 to 2018. The star varied between R=11.4 and 14.2 mag with a time scale of 500 days. An appreciable color variation was observed, the star being bluer when brighter. H emission was present around maxima. The spectrum is that of an N type giant veiled by a variable dusty envelope
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