84 research outputs found
Double-nucleus elliptical MCG-01-12-005 in an X-ray emitting cluster of galaxies
The scenario of galaxy formation is believed to follow a structure that
builds up from the bottom, with large galaxies being formed by several merging
episodes of smaller ones. In this scenario a number of galaxies can be expected
to be seen in the merging phase, with their external regions already mixed,
while their nuclei, with stronger self-gravitation, are still recognizable as
such. During a photometric monitoring of AGNs in the field of a long-exposure
INTEGRAL pointing, we serendipitously found an elliptical galaxy in the center
of the X-ray cluster (EXO 0422-086) with two nuclei. We performed surface
photometry on our images and those of the SDSS archive and obtained slit
spectra of both nuclei. Aperture photometry of the two stellar-like nuclei
showed very similar colors in the SDSS image and in our Johnson BVRI images,
which is typical of an elliptical galaxy nucleus. The spectra of the nuclei
showed the typical absorption lines of an elliptical galaxy without appreciable
emission lines. The redshifts derived from each nucleus were equal and fully
consistent with the literature value (0.0397). We can therefore exclude the
possibility that one of the nuclei is a foreground star or a background AGN and
consider this elliptical galaxy as a bona fide example of a galaxy merger.Comment: 4 pages, 3 figures. Accepted on Astronomy and Astrophysic
On the nature of V2282 Sgr
The star V2282 Sgr is positionally consistent with a strong Chandra X-ray and
a Spitzer/IRAC MIR source. We derived its long term -band light curve from
the photographic archives of the Asiago and Catania Observatories, covering the
years from 1965 to 1984. CCD photometry in Summer 2009 was re-analyzed.
Optical spectra were secured at Loiano Observatory in 2011 and 2012. J H K
photometry, obtained from several experiments in different epochs was compared
and the Spitzer images were re-analyzed.
V2282 Sgr was found to be irregular variable in all wavelengths.
Spectroscopically, it shows strong emission features (H Balmer lines, [NII]6584
AA and [OIII]5007/4959 AA) while the Na D doublet is very strong, indicating a
circumstellar envelope. A single thermal energy distribution cannot reproduce
the observed SED, while it can be explained as the sum of a G-type star plus a
variable circumstellar disc, which mimics a class 0/I object. Most likely,
V2282 Sgr is a 1-2 mass pre main sequence star with an accretion
disk.Comment: 13 pages, 7 figure, in press on Baltic Astronom
ASASSN-18aan revisited
The light curve of the cataclismic variable ASASSN-18aan is studied using
recent observations of the MC589 Observatory, giving an orbital Period and
Epoch fully consistent with the data obtained after the discovery flare in
2018. Archival data from ASASSN, ZTF and Gaia were used to check if its flares
have a quasi-periodic behaviour. A recurrency time scale of about 11 months is
found, confirming a previous tentative result using the historic plate archive
of the Asiago Observatory. The next outbursts are expected by April 2023 and
March 2024.Comment: 7 pages, 2 figures, published on OEJ
Spectral Slope Variability of BL Lac Objects in the Optical Band
Light curves of eight BL Lac objects in the BVRI bands have been analyzed.
All of the objects tend to be bluer when brighter. However spectral slope
changes differ quantitatively from those of a sample of QSOs analyzed in a
previous paper (Trevese & Vagnetti 2002) and appear consistent with a different
nature of the optical continuum. A simple model representing the variability of
a synchrotron component can explain the spectral changes. Constraints on a
possible thermal accretion disk component contributing to the optical
luminosity are discussed.Comment: 15 pages, 5 figures, to appear in ApJ, June 200
A New Fast Silicon Photomultiplier Photometer
The realization of low-cost instruments with high technical performance is a
goal which deserves some efforts in an epoch of fast technological
developments: indeed such instruments can be easily reproduced and therefore
allow to open new research programs in several Observatories. We realized a
fast optical photometer based on the SiPM technology, using commercially
available modules. Using low-cost components we have developed a custom
electronic chain to extract the signal produced by a commercial MPPC module
produced by Hamamatsu, in order to obtain sub millisecond sampling of the light
curve of astronomical sources, typically pulsars. In the early February 2011 we
observed the Crab Pulsar at the Cassini telescope with our prototype
photometer, deriving its period, power spectrum and shape of its light curve in
very good agreement with the results obtained in the past with other
instruments.Comment: Accepted for Publications of the Astronomical Society of Pacific
(PASP), 8 pages, 8 figure
SiFAP: A New Fast Astronomical Photometer
A fast photometer based on SiPM technology was developed and tested at the University of Rome "La Sapienza" and at the Bologna Observatory. In this paper we present the improvements applied to our instrument, concerning new cooled sensors, a new version of the electronics and an upgraded control timing software
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