1,997 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
Spectroscopy and BVI photometry of the young open cluster NGC 6604
BVI photometry (from South Africa Astron. Obs.), Echelle high resolution
spectroscopy and AFOSC integral field spectroscopy (from Asiago, Italy) of the
young open cluster NGC 6604 are presented. Age, distance, reddening,
membership, radial and rotational velocities are derived and discussed. An age
of 5 million years, a distance of 1.7 kpc and a reddening E(B-V)=1.02 are
found. The cluster radial velocity is in agreement with the Hron (1987) model
for the Galaxy disk rotation. Pre-ZAMS objects are not present down to M_V =
+1.5 mag.Comment: accepted in Astron.Astrophys.Suppl. Figure 2 is degraded in
resolutio
The new carbon symbiotic star IPHAS J205836.43+503307.2
We are performing a search for symbiotic stars using IPHAS, the INT Halpha
survey of the northern Galactic plane, and follow-up observations. Candidate
symbiotic stars are selected on the basis of their IPHAS and near-IR colours,
and spectroscopy and photometry are obtained to determine their nature. We
present here observations of the symbiotic star candidate IPHAS
J205836.43+503307.2. The optical spectrum shows the combination of a number of
emission lines, among which are the high-excitation species of [OIII], HeII,
[Ca V], and [Fe VII], and a red continuum with the features of a star at the
cool end of the carbon star sequence. The nebular component is spatially
resolved: the analysis of the spatial profile of the [NII]6583 line in the
spectrum indicates a linear size of ~2.5 arcsec along the east-west direction.
Its velocity structure suggests an aspherical morphology. The near-infrared
excess of the source, which was especially strong in 1999, indicated that a
thick circumstellar dust shell was also present in the system. The carbon star
has brightened in the last decade by two to four magnitudes at red and
near-infrared wavelengths. Photometric monitoring during a period of 60 days
from November 2010 to January 2011 reveals a slow luminosity decrease of 0.2
magnitudes. From the observed spectrophotometric properties and variability, we
conclude that the source is a new Galactic symbiotic star of the D-type, of the
rare kind that contains a carbon star, likely a carbon Mira. Only two other
systems of this type are known in the Galaxy.Comment: 6 pages, 4 figure
Improving fast generation of halo catalogs with higher-order Lagrangian perturbation theory
We present the latest version of Pinocchio, a code that generates catalogues
of DM haloes in an approximate but fast way with respect to an N-body
simulation. This code version extends the computation of particle and halo
displacements up to 3rd-order Lagrangian Perturbation Theory (LPT), in contrast
with previous versions that used Zeldovich approximation (ZA).
We run Pinocchio on the same initial configuration of a reference N-body
simulation, so that the comparison extends to the object-by-object level. We
consider haloes at redshifts 0 and 1, using different LPT orders either for
halo construction - where displacements are needed to decide particle accretion
onto a halo or halo merging - or to compute halo final positions.
We compare the clustering properties of Pinocchio haloes with those from the
simulation by computing the power spectrum and 2-point correlation function
(2PCF) in real and redshift space (monopole and quadrupole), the bispectrum and
the phase difference of halo distributions. We find that 2LPT and 3LPT give
noticeable improvement. 3LPT provides the best agreement with N-body when it is
used to displace haloes, while 2LPT gives better results for constructing
haloes. At the highest orders, linear bias is typically recovered at a few per
cent level.
In Fourier space and using 3LPT for halo displacements, the halo power
spectrum is recovered to within 10 per cent up to Mpc. The
results presented in this paper have interesting implications for the
generation of large ensemble of mock surveys aimed at accurately compute
covariance matrices for clustering statistics.Comment: 20 pages, 20 figures, submitted to MNRA
- …