27 research outputs found
Environment of 1 ≤ z ≤ 2 MIR selected obscured and unobscured AGNs in the Extended Chandra Deep Field South
Context. In unified models, different types of active galaxy nuclei (AGN) correspond to a single class of objects, where their observed differences are solely due to the different orientations of the obscuring material around the central inner regions. Recent studies also show that this obscuring material can even extend at galactic scales due to debris from galaxy interactions and/or mergers. In standard unified models the different AGN types are expected to show similar galaxy environments. Aims. We aim to investigate properties and environment of obscured and unobscured AGNs selected from mid-infrared (MIR) bands from the Multiwavelength Survey by Yale-Chile (MUSYC), in order to test the unified model and evolutionary scenarios. Methods. The sample of AGNs was selected from images obtained with the Infrared Array Camera (IRAC) mounted on the Spitzer Space Telescope, based on their MIR colors centered at wavelengths [3.6], [4.5], [5.8] and [8.0] microns. We selected two samples of AGNs with redshifts in the range 1 ≤ z ≤ 2 and rest-frame absolute magnitudes Mv ≤ -21: obscured and unobscured AGNs by means of a simple optical-MIR color cut criterion (R - [4:5] = 3:05.) Results. We find that obscured AGNs are intrinsically optically faint in the R band, suggesting that luminous IR-selected AGNs have a significant dust extinction. From a cross-correlation with several X-ray surveys, we find that the majority of the AGNs in our sample have X-ray luminosities similar to those found in Seyfert-like galaxies. We study the properties of galaxies surrounding these two samples. Neighbouring galaxies located close to (~200 kpc) obscured AGNs tend to have redder colors, compared to the local environment of unobscured AGNs. Results obtained from a KS test show that the two color distributions are different at ~95% confidence level. We find that obscured AGNs are located in denser local galaxy environments compared to the unobscured AGN sample. Conclusions. Our results suggest that AGN obscuration can occur at galactic scales, possibly due to galaxy interactions or mergers, and that the simple unified model based solely on the local torus orientation may not be sufficient to explain all the observations.Fil: Bornancini, Carlos Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Taormina, Mónica Silvia. Polish Academy of Sciences. Nicolaus Copernicus Astronomical Center; Polonia. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; ArgentinaFil: Garcia Lambas, Diego Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentin
Environment and properties of obscured and unobscured active galactic nuclei
Abstract: We analyze the properties of obscured and unobscured active galactic nuclei selected using mid-infrared colors in the redshift range 1 < z < 3. We find that obscured objects are located in a denser local galaxy environment compared to the unobscured sample.We analyze the properties of obscured and unobscured active galactic nuclei selected using mid-infrared colors in the redshift range 1 < z < 3. We find that obscured objects are located in a denser local galaxy environment compared to the unobscured sample.http://adsabs.harvard.edu/abs/2013AAABS...4..153TFil: Taormina, Mónica. Conicet. Instituto de Astronomía Teórica y Experimental; Argentina.Fil: Bornancini, Carlos Guillermo. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina.Fil: Bornancini, Carlos Guillermo. Conicet. Instituto de Astronomía Teórica y Experimental; Argentina.Astronomía (incluye Astrofísica y Ciencias del Espacio
The dynamical mass and evolutionary status of the type-II Cepheid in the eclipsing binary system OGLE-LMC-T2CEP-211 with a double-ring disk
We present the analysis of a peculiar W~Virginis (pWVir) type-II Cepheid,
OGLE-LMC-T2CEP-211 (), in a double-lined binary system
(), which shed light on virtually unknown evolutionary status
and structure of pWVir stars. The dynamical mass of the Cepheid (first ever for
a type-II Cepheid) is and the radius
. The companion is a massive ()
main-sequence star obscured by a disk. Such configuration suggests a mass
transfer in the system history. We found that originally the system
() was composed of and stars, with
the current Cepheid being more massive. The system age is now 200 My,
and the Cepheid is almost completely stripped of hydrogen, with helium mass of
of the total mass. It finished transferring the mass 2.5 My ago
and is evolving towards lower temperatures passing through the instability
strip. Comparison with observations indicate a reasonable
mass loss from the Cepheid. The companion is
most probably a Be main-sequence star with and .
Our results yield a good agreement with a pulsation theory model for a
hydrogen-deficient pulsator, confirming the described evolutionary scenario. We
detected a two-ring disk () and a shell
() around the companion, that is probably a
combination of the matter from the past mass transfer, the mass being lost by
the Cepheid due to wind and pulsations, and a decretion disk around a rapidly
rotating secondary. Our study together with observational properties of pWVir
stars suggests that their majority are products of a similar binary evolution
interaction.Comment: 21 pages, 14 figures, 6 tables, accepted for publication in Ap
Mass and p-factor of the type II Cepheid OGLE-LMC-T2CEP-098 in a binary system
We present the results of a study of the type II Cepheid () in the eclipsing binary system OGLE-LMC-T2CEP-098 ().
The Cepheid belongs to the peculiar W Vir group, for which the evolutionary
status is virtually unknown. It is the first single-lined system with a
pulsating component analyzed using the method developed by Pilecki et al.
(2013). We show that the presence of a pulsator makes it possible to derive
accurate physical parameters of the stars even if radial velocities can be
measured for only one of the components. We have used four different methods to
limit and estimate the physical parameters, eventually obtaining precise
results by combining pulsation theory with the spectroscopic and photometric
solutions. The Cepheid radius, mass and temperature are ,
and , respectively, while its companion
has similar size (), but is more massive () and
hotter (). Our best estimate for the p-factor of the Cepheid is . The mass, position on the period-luminosity diagram, and pulsation
amplitude indicate that the pulsating component is very similar to the
Anomalous Cepheids, although it has a much longer period and is redder in
color. The very unusual combination of the components suggest that the system
has passed through a mass transfer phase in its evolution. More complicated
internal structure would then explain its peculiarity.Comment: 23 pages, 17 figures, accepted for publication in Ap
Cepheids with giant companions. I. Revealing a numerous population of double-lined binary Cepheids
Masses of classical Cepheids of 3 to 11 M are predicted by theory but
those measured, clump between 3.6 and 5 M. As a result, their
mass-luminosity relation is poorly constrained, impeding our understanding of
basic stellar physics and the Leavitt Law. All Cepheid masses come from the
analysis of 11 binary systems, including only 5 double-lined and well-suited
for accurate dynamical mass determination. We present a project to analyze a
new, numerous group of Cepheids in double-lined binary (SB2) systems to provide
mass determinations in a wide mass interval and study their evolution. We
analyze a sample of 41 candidate binary LMC Cepheids spread along the P-L
relation, that are likely accompanied by luminous red giants, and present
indirect and direct indicators of their binarity. In a spectroscopic study of a
subsample of 18 brightest candidates, for 16 we detected lines of two
components in the spectra, already quadrupling the number of Cepheids in SB2
systems. Observations of the whole sample may thus lead to quadrupling all the
Cepheid mass estimates available now. For the majority of our candidates,
erratic intrinsic period changes dominate over the light travel-time effect due
to binarity. However, the latter may explain the periodic phase modulation for
4 Cepheids. Our project paves the way for future accurate dynamical mass
determinations of Cepheids in the LMC, Milky Way, and other galaxies, which
will potentially increase the number of known Cepheid masses even 10-fold,
hugely improving our knowledge about these important stars.Comment: 12 pages, 7 figures, 3 tables, accepted for publication in Ap
Discovery of a binary-origin classical Cepheid in a binary system with a 59-day orbital period
We report the discovery of a surprising binary configuration of the
double-mode Cepheid OGLE-LMC-CEP-1347 pulsating in the first (P_1=0.690d) and
second overtone (P_2=0.556d) modes. The orbital period (P_orb=59d) of the
system is five times shorter than the shortest known to date (310d) for a
binary Cepheid. The Cepheid itself is also the shortest-period one ever found
in a binary system and the first double-mode Cepheid in a spectroscopically
double-lined binary. OGLE-LMC-CEP-1347 is most probably on its first crossing
through the instability strip, as inferred from both its short period and fast
period increase, consistent with evolutionary models, and from the short
orbital period (not expected for binary Cepheids whose components have passed
through the red giant phase). Our evolutionary analysis yielded a
first-crossing Cepheid with a mass in a range of 2.9-3.4 Msun (lower than any
measured Cepheid mass), consistent with observations. The companion is a stable
star, at least two times fainter and less massive than the Cepheid (preliminary
mass ratio q=0.55), while also redder and thus at the subgiant or more advanced
evolutionary stage. To match these characteristics, the Cepheid has to be a
product of binary interaction, most likely a merger of two less massive stars,
which makes it the second known classical Cepheid of binary origin. Moreover,
further evolution of the components may lead to another binary interaction.Comment: 6 pages, 4 figures, 1 table, published in The Astrophysical Journal
Letter
Distance scale calibration based on early-type binaries
Our main goal is to establish a firm empirical calibration of the surface brightness vs. (V-K) color relation for early type stars based on high quality spectroscopic and infrared observations of early-type detached eclipsing systems in the Large Magellanic Cloud (LMC). Our calibration of this relation will allow distance determinations accurate to about 2.5% to a single object located well beyond the Magellanic Clouds. This will let us calibrate other distance indicators, including period-luminosity relations for Cepheids. The first step of the project is to determine precise parameters for a sample of B-type systems in the LMC. We have already made a preliminary analysis of light and radial velocity curves for selected objects and measured their masses and radii. Here we present the results for one such system
Distance scale calibration based on early-type binaries
Our main goal is to establish a firm empirical calibration of the surface brightness vs. (V-K) color relation for early type stars based on high quality spectroscopic and infrared observations of early-type detached eclipsing systems in the Large Magellanic Cloud (LMC). Our calibration of this relation will allow distance determinations accurate to about 2.5% to a single object located well beyond the Magellanic Clouds. This will let us calibrate other distance indicators, including period-luminosity relations for Cepheids. The first step of the project is to determine precise parameters for a sample of B-type systems in the LMC. We have already made a preliminary analysis of light and radial velocity curves for selected objects and measured their masses and radii. Here we present the results for one such system