11 research outputs found
Trident: A three-pronged galaxy survey. I. Lyman alpha emitting galaxies at z~2 in GOODS North
Context. Lyman alpha emitting galaxies (LAEs) are used to probe the distant
universe and are therefore important for galaxy evolution studies and for
providing clues to the nature of the epoch of reionization, but the exact
circumstances under which Lyman alpha escapes a galaxy are still not fully
understood.
Aims. The Trident project is designed to simultaneously examine Lyman alpha,
H-alpha and Lyman Continuum emission from galaxies at redshift z~2, thus
linking together these three aspects of ionising radiation in galaxies. In this
paper, we outline the strategy of this project and examine the properties of
LAEs in the GOODS North field.
Methods. We performed a narrowband LAE survey in GOODS North using existing
and two custom made filters at the Nordic Optical Telescope with MOSCA. We use
complementary broad band archival data in the field to make a careful candidate
selection and perform optical to near-IR SED fitting. We also estimate
far-infrared luminosities by matching our candidates to detections in
Spitzer/MIPS 24{\mu}m and Herschel/PACS catalogs.
Results. We find a total of 25 LAE candidates, probing mainly the bright end
of the LAE luminosity function with L_Ly {\alpha} ~ 1-15e42 erg/s. They display
a range of masses of ~0.5-50e9 M_solar, and average ages from a few tens of Myr
to 1 Gyr when assuming a constant star formation history. The majority of our
candidates also show signs of recent elevated star formation. Three candidates
have counterparts in the GOODS-Herschel far-IR catalogue, with luminosities
consistent with ultra-luminous infrared galaxies (ULIRGs).
Conclusions. The wide range of parameters derived from our SED fitting, as
well as part of our sample being detected as ULIRGs, seems to indicate that at
these Lyman alpha luminosities, LAEs do not necessarily have to be young
dwarfs, and that a lack of dust is not required for Lyman alpha to escape.Comment: 16 pages, 12 figures. Accepted version for publication in A&
Recent activity of the Be/X-ray binary system SAX J2103.5+4545
Aims. We present a multiwavelength study of the Be/X-ray binary system SAX
J2103.5+4545 with the goal of better characterizing the transient behaviour of
this source.
Methods. SAX J2103.5+4545 was observed by Swift-XRT four times in 2007 from
April 25 to May 5, and during quiescence in 2012 August 31. In addition, this
source has been monitored from the ground-based astronomical observatories of
El Teide (Tenerife, Spain), Roque de los Muchachos (La Palma, Spain) and Sierra
Nevada (Granada, Spain) since 2011 August, and from the TUBITAK National
Observatory (Antalya, Turkey) since 2009 June. We have performed spectral and
photometric temporal analyses in order to investigate the different states
exhibited by SAX J2103.5+4545.
Results. In X-rays, an absorbed power law model provided the best fit for all
the XRT spectra. An iron-line feature at ~6.42 keV was present in all the
observations except for that taken during quiescence in 2012. The photon
indexes are consistent with previous studies of SAX J2103.5+4545 in high/low
luminosity states. Pulsations were found in all the XRT data from 2007
(2.839(2) mHz; MJD 54222.02), but not during quiescence. Both optical outbursts
in 2010 and 2012 lasted for about 8/9 months (as the one in 2007 probably did
and the current one in 2014 might do) and were most probably caused by mass
ejection events from the Be star that eventually fed the circumstellar disc.
All of these outbursts started about 3 months before the triggering of the
X-ray activity, and about the same period before the maximum of the H_alpha
line equivalent width (in emission) was reached at only ~ -5 \AA. In this work
we found that the global correlation between the BV variability and the X-ray
intensity was also observed at longer wavelengths in the IR domain.Comment: 11 pages, 7 figures, and online material (2 tables). Submitted to A&A
in 2014 Januar
Detection of a large Be circumstellar disk during X-ray quiescence of XTE J1946+274
We present a multiwavelength study of the Be/X-ray binary system XTE
J1946+274 with the main goal of better characterizing its behavior during X-ray
quiescence. We aim to shed light on the mechanism which triggers the X-ray
activity for this source. XTE J1946+274 was observed by Chandra-ACIS during
quiescence in 2013 March 12. In addition, this source has been monitored from
the ground-based astronomical observatories of El Teide (Tenerife, Spain),
Roque de los Muchachos (La Palma, Spain) and Sierra Nevada (Granada, Spain)
since 2011 September, and from the TUBITAK National Observatory (Antalya,
Turkey) since 2005 April. We have performed spectral and photometric temporal
analyses in order to investigate the quiescent state and transient behavior of
this binary system. In 2006, a long mass ejection event took place from the Be
star, lasting for about seven years. We also found that a large Be
circumstellar disk was present during quiescence, although major X-ray activity
was not observed. We made an attempt to explain this scenario by assuming the
permanently presence of a tilted and warped Be circumstellar disk. The 0.3-10
keV X-ray spectrum during quiescence was well fitted with either an absorbed
blackbody or absorbed power-law models. The main parameters obtained for these
models were kT=1.43+/-0.17 and Gamma=0.9+/-0.4 (with N_H~2-7E+22 cm-2). The
0.3-10 keV flux of the source was ~0.8E-12 erg-1 cm-2 s-1. Pulsations were
found with P_pulse=15.757(1) s (MJD 56363.115) and an rms pulse fraction of
32.1(3)%. The observed X-ray luminosity during quiescent periods may be
explained by the neutron star being in supersonic propeller regimen.Comment: 9 pages, 7 figures, accepte
A subsynchronously rotating pulsating subdwarf B star in a short-period binary with a white dwarf companion
We present our analysis of KIC 7664467, an sdB pulsator that we have found to be residing in a 1.56-day binary system with a white-dwarf companion. This system was observed photometrically with the Kepler spacecraft and spectroscopically with ground-based telescopes. We analyzed the amplitude spectra detecting 61 periods, rotationally split multiplets, and an equally spaced sequence in period. These two features helped with the mode identification. We derived both the binary and rotation periods showing that this is another binary system with a subsynchronous sdB star. From our spectroscopy of the sdB star, we determined Teff = 27440 ± 120 K, log g = 5.38 ± 0.02 dex. The abundance pattern follows the general trend observed in sdB stars, where light metals are subsolar, while the Fe abundance is very close to the solar value. We found the N enrichment and low abundances of C and O that resemble the equilibrium abundances of the CNO cycle. We could also measure the Mg and Si abundances. Using the radial velocity amplitude K1 = 57(3) km s-1 and the Doppler boosting-dominated photometric signal at the orbital period, we constrained the companion to be a compact object, almost certainly a white dwarf
Activity from the Be/X-ray binary system V0332+53 during its intermediate-luminosity outburst in 2008
Aims. We present a study of the Be/X-ray binary system V 0332+53 with the main goal of characterizing its behaviour mainly during the intermediate-luminosity X-ray event in 2008. In addition, we aim to contribute to the understanding of the behaviour of the donor companion by including optical data from our dedicated campaign starting in 2006. Methods. V 0332+53 was observed by RXTE and Swift during the decay of the intermediate-luminosity X-ray outburst of 2008, and with Suzaku before the rising of the third normal outburst of the 2010 series. In addition, we present recent data from the Spanish ground-based astronomical observatories of El Teide (Tenerife), Roque de los Muchachos (La Palma), and Sierra Nevada (Granada), and since 2006 from the Turkish TÜB °TAK National Observatory (Antalya). We have performed temporal analyses to investigate the transient behaviour of this system during several outbursts. Results. Our optical study revealed that continuous mass ejection episodes from the Be star have been taking place since 2006 and another is currently ongoing. The broad-band 1-60 keV X-ray spectrum of the neutron star during the decay of the 2008 outburst was well fitted with standard phenomenological models that were enhanced by an absorption feature of unknown origin at about 10 keV and a narrow iron K-alpha fluorescence line at 6.4 keV. For the first time in V 0332+53 we tentatively see an increase in the cyclotron line energy with increasing flux (although further and more sensitive observations are needed to confirm this). The fast aperiodic variability shows a quasi-periodic oscillation (QPO) at 227 ± 9 mHz only during the lowest luminosities, which might indicate that the inner regions surrounding the magnetosphere are more visible during the lowest flux states.M.C.G. acknowledges support by the European social fund within the framework of realizing the project >Support of inter-sectoral mobility and quality enhancement of research teams at Czech Technical University in Prague>, CZ.1.07/2.3.00/30.0034
Asteroseismology revealing trapped modes in KIC 10553698A
The subdwarf-B pulsator, KIC 10553698A, is one of 16 such objects observed with a one-minute sampling rate for most of the duration of the Kepler mission. Like most of these stars, it displays a rich g-mode pulsation spectrum with several clear multiplets that maintain regular frequency splitting. We identify these pulsation modes as components of rotationally split multiplets in a star rotating with a period of ~41 d. From 162 clearly significant periodicities, we are able to identify 156 as likely components of ℓ = 1 or ℓ = 2 multiplets. For the first time we are able to detect ℓ = 1 modes that interpose in the asymptotic period sequences and that provide a clear indication of mode trapping in a stratified envelope, as predicted by theoretical models. A clear signal is also present in the Kepler photometry at 3.387 d. Spectroscopic observations reveal a radial-velocity amplitude of 64.8 km s-1. We find that the radial-velocity variations and the photometric signal have phase and amplitude that are perfectly consistent with a Doppler-beaming effect and conclude that the unseen companion, KIC 10553698B, must be a white dwarf most likely with a mass close to 0.6 M⊙
Activity from the Be/X-ray binary system V0332+53 during its intermediate-luminosity outburst in 2008
Aims. We present a study of the Be/X-ray binary system V 0332+53 with the main goal of characterizing its behaviour mainly during the intermediate-luminosity X-ray event in 2008. In addition, we aim to contribute to the understanding of the behaviour of the donor companion by including optical data from our dedicated campaign starting in 2006.
Methods. V 0332+53 was observed by RXTE and Swift during the decay of the intermediate-luminosity X-ray outburst of 2008, and with Suzaku before the rising of the third normal outburst of the 2010 series. In addition, we present recent data from the Spanish ground-based astronomical observatories of El Teide (Tenerife), Roque de los Muchachos (La Palma), and Sierra Nevada (Granada), and since 2006 from the Turkish TÃœBÄ°TAK National Observatory (Antalya). We have performed temporal analyses to investigate the transient behaviour of this system during several outbursts.
Results. Our optical study revealed that continuous mass ejection episodes from the Be star have been taking place since 2006 and another is currently ongoing. The broad-band 1–60 keV X-ray spectrum of the neutron star during the decay of the 2008 outburst was well fitted with standard phenomenological models that were enhanced by an absorption feature of unknown origin at about 10 keV and a narrow iron K-alpha fluorescence line at 6.4 keV. For the first time in V 0332+53 we tentatively see an increase in the cyclotron line energy with increasing flux (although further and more sensitive observations are needed to confirm this). The fast aperiodic variability shows a quasi-periodic oscillation (QPO) at 227 ± 9 mHz only during the lowest luminosities, which might indicate that the inner regions surrounding the magnetosphere are more visible during the lowest flux states
Asteroseismology revealing trapped modes in KIC 10553698A
The subdwarf-B pulsator, KIC 10553698A, is one of 16 such objects observed
with one-minute sampling for most of the duration of the Kepler Mission. Like
most of these stars, it displays a rich g-mode pulsation spectrum with several
clear multiplets that maintain regular frequency splitting. We identify these
pulsation modes as components of rotationally split multiplets in a star
rotating with a period of about 41 d. From 162 clearly significant
periodicities, we are able to identify 156 as likely components of l=1 or l=2
multiplets. For the first time we are able to detect l=1 modes that interpose
in the asymptotic period sequences and that provide a clear indication of mode
trapping in a stratified envelope, as predicted by theoretical models. A clear
signal is also present in the Kepler photometry at 3.387 d. Spectroscopic
observations reveal a radial-velocity amplitude of 64.8 km/s. We find that the
radial-velocity variations and the photometric signal have phase and amplitude
that are perfectly consistent with a Doppler-beaming effect and conclude that
the unseen companion, KIC 10553698B, must be a white dwarf most likely with a
mass close to 0.6 solar masses.Comment: 14 pages, 12 figures. Accepted for publication in A&
Activity from the Be/X-ray binary system V0332+53 during its intermediate-luminosity outburst in 2008
Aims: We present a study of the Be/X-ray binary system V 0332+53 with the
main goal of characterizing its behavior mainly during the
intermediate-luminosity X-ray event on 2008. In addition, we aim to contribute
to the understanding of the global behavior of the donor companion by including
optical data from our dedicated campaign starting on 2006. Methods: V 0332+53
was observed by RXTE and Swift during the decay of the intermediate-luminosity
X-ray outburst of 2008, as well as with Suzaku before the rising of the third
normal outburst of the 2010 series. In addition, we present recent data from
the Spanish ground-based astronomical observatories of El Teide (Tenerife),
Roque de los Muchachos (La Palma), and Sierra Nevada (Granada), and since 2006
from the Turkish TUBITAK National Observatory (Antalya). We have performed
temporal analyses to investigate the transient behaviour of this system during
several outbursts. Results: Our optical study revealed that continuous mass
ejection episodes from the Be star have been taking place since 2006 and
another one is currently ongoing. The broad-band 1-60 keV X-ray spectrum of the
neutron star during the decay of the 2008 outburst was well fitted with
standard phenomenological models, enhanced by an absorption feature of unknown
origin at about 10 keV and a narrow iron K-alpha fluorescence line at 6.4 keV.
For the first time in V 0332+53 we tentatively see an increase of the cyclotron
line energy with increasing flux (although further and more sensitive
observations are needed to confirm this). Regarding the fast aperiodic
variability, we detect a Quasi-Periodic Oscillation (QPO) at 227+-9 mHz only
during the lowest luminosities. The latter fact might indicate that the inner
regions surrounding the magnetosphere are more visible during the lowest flux
states.Comment: Accepted for publication in A&A (13/01/16