178 research outputs found
The night-sky at the Calar Alto Observatory
We present a characterization of the main properties of the night-sky at the
Calar Alto observatory for the time period between 2004 and 2007. We use
optical spectrophotometric data, photometric calibrated images taken in
moonless observing periods, together with the observing conditions regularly
monitored at the observatory, such as atmospheric extinction and seeing. We
derive, for the first time, the typical moonless night-sky optical spectrum for
the observatory. The spectrum shows a strong contamination by different
pollution lines, in particular from Mercury lines, which contribution to the
sky-brightness in the different bands is of the order of ~0.09 mag, ~0.16 mag
and ~0.10 mag in B, V and R respectively. The zenith-corrected values of the
moonless night-sky surface brightness are 22.39, 22.86, 22.01, 21.36 and 19.25
mag arcsec^-2 in U, B, V, R and I, which indicates that Calar Alto is a
particularly dark site for optical observations up to the I-band. The fraction
of astronomical useful nights at the observatory is ~70%, with a ~30% of
photometric nights. The typical extinction at the observatory is k_V~0.15 mag
in the Winter season, with little dispersion. In summer the extinction has a
wider range of values, although it does not reach the extreme peaks observed at
other sites. The median seeing for the last two years (2005-6) was ~0.90",
being smaller in the Summer (~0.87") than in the Winter (~0.96"). We conclude
in general that after 26 years of operations Calar Alto is still a good
astronomical site, being a natural candidate for future large aperture optical
telescopes.Comment: 16 pages, 5 figures, accepted for publishing in the Publications of
Astronomical Society of the Pacific (PASP
GIANO-TNG spectroscopy of red supergiants in the young star cluster RSGC3
The Scutum complex in the inner disk of the Galaxy has a number of young star
clusters dominated by red supergiants that are heavily obscured by dust
extinction and observable only at infrared wavelengths. These clusters are
important tracers of the recent star formation and chemical enrichment history
in the inner Galaxy. During the technical commissioning and as a first science
verification of the GIANO spectrograph at the Telescopio Nazionale Galileo, we
secured high-resolution (R=50,000) near-infrared spectra of five red
supergiants in the young Scutum cluster RSGC3. Taking advantage of the full
YJHK spectral coverage of GIANO in a single exposure, we were able to measure
several tens of atomic and molecular lines that were suitable for determining
chemical abundances. By means of spectral synthesis and line equivalent width
measurements, we obtained abundances of Fe and iron-peak elements such as Ni,
Cr, and Cu, alpha (O, Mg, Si, Ca, Ti), other light elements (C, N, F, Na, Al,
and Sc), and some s-process elements (Y, Sr). We found average half-solar iron
abundances and solar-scaled [X/Fe] abundance patterns for most of the elements,
consistent with a thin-disk chemistry. We found depletion of [C/Fe] and
enhancement of [N/Fe], consistent with standard CN burning, and low 12C/13C
abundance ratios (between 9 and 11), which require extra-mixing processes in
the stellar interiors during the post-main sequence evolution. We also found
local standard of rest V(LSR)=106 km/s and heliocentric V(HEL)=90 km/s radial
velocities with a dispersion of 2.3 km/s. The inferred radial velocities,
abundances, and abundance patterns of RSGC3 are very similar to those
previously measured in the other two young clusters of the Scutum complex,
RSGC1 and RSGC2, suggesting a common kinematics and chemistry within the Scutum
complex
GIANO-TNG spectroscopy of red supergiants in the young star cluster RSGC2
The inner disk of the Galaxy has a number of young star clusters dominated by
red supergiants that are heavily obscured by dust extinction and observable
only at infrared wavelengths. These clusters are important tracers of the
recent star formation and chemical enrichment history in the inner Galaxy.
During the technical commissioning and as a first science verification of the
GIANO spectrograph at the Telescopio Nazionale Galileo, we secured
high-resolution (R~50,000) near-infrared spectra of three red supergiants in
the young Scutum cluster RSGC2. Taking advantage of the full YJHK spectral
coverage of GIANO in a single exposure, we were able to identify several tens
of atomic and molecular lines suitable for chemical abundance determinations.
By means of spectral synthesis and line equivalent width measurements, we
obtained abundances of Fe and other iron-peak elements such as V, Cr, Ni, of
alpha (O, Mg, Si, Ca and Ti) and other light elements (C, N, Na, Al, K, Sc),
and of some s-process elements (Y, Sr). We found iron abundances between half
and one third solar and solar-scaled [X/Fe] abundance patterns of iron-peak,
alpha and most of the light elements, consistent with a thin-disk chemistry. We
found a depletion of [C/Fe] and enhancement of [N/Fe], consistent with CN
burning, and low 12C/13C abundance ratios (between 9 and 11), requiring
extra-mixing processes in the stellar interiors during the post-main sequence
evolution. Finally, we found a slight [Sr/Fe] enhancement and a slight [Y/Fe]
depletion (by a factor of <=2), with respect to solar.Comment: Paper accepted on A&
Lines and continuum sky emission in the near infrared: observational constraints from deep high spectral resolution spectra with GIANO-TNG
Aims Determining the intensity of lines and continuum airglow emission in the
H-band is important for the design of faint-object infrared spectrographs.
Existing spectra at low/medium resolution cannot disentangle the true
sky-continuum from instrumental effects (e.g. diffuse light in the wings of
strong lines). We aim to obtain, for the first time, a high resolution infrared
spectrum deep enough to set significant constraints on the continuum emission
between the lines in the H-band. Methods During the second commissioning run of
the GIANO high-resolution infrared spectrograph at La Palma Observatory, we
pointed the instrument directly to the sky and obtained a deep spectrum that
extends from 0.97 to 2.4 micron. Results The spectrum shows about 1500 emission
lines, a factor of two more than in previous works. Of these, 80% are
identified as OH transitions; half of these are from highly excited molecules
(hot-OH component) that are not included in the OH airglow emission models
normally used for astronomical applications. The other lines are attributable
to O2 or unidentified. Several of the faint lines are in spectral regions that
were previously believed to be free of line emission. The continuum in the
H-band is marginally detected at a level of about 300
photons/m^2/s/arcsec^2/micron, equivalent to 20.1 AB-mag/arcsec^2. The observed
spectrum and the list of observed sky-lines are published in electronic format.
Conclusions Our measurements indicate that the sky continuum in the H-band
could be even darker than previously believed. However, the myriad of airglow
emission lines severely limits the spectral ranges where very low background
can be effectively achieved with low/medium resolution spectrographs. We
identify a few spectral bands that could still remain quite dark at the
resolving power foreseen for VLT-MOONS (R ~6,600).Comment: 7 pages, 4 figures, to be published in Astronomy & Astrophysic
A FIRST-APM-SDSS survey for high-redshift radio QSOs
We selected from VLA-FIRST a sample of 94 objects starlike in SDSSS, and with
APM colour O-E>2, i.e. consistent with their being high-z QSOs. 78 candidates
were classified spectroscopically from published data (mainly SDSS) or
observations reported here. The fractions of QSOs (51/78) and z > 3 QSOs
(23/78) are comparable to those found in other photometric searches for high-z
QSOs. We confirm that O-E>2 ensures inclusion of all QSOs with 3.7 < z < 4.4.
The fraction of broad absorption line (BAL) QSOs for 2 < z < 4.4 is 27+-10 per
cent (7/26), and the estimated BAL fraction for radio loud (RL) QSOs is at
least as high as for optically selected QSOs (about 13 per cent). The high BAL
fraction and the high fraction of LoBALs in our sample are likely due to the
red colour selection. The space density of RL QSOs for 3.7 < z < 4.4, MAB (1450
A) 10^25.7 W Hz^(-1) is 1.7+-0.6 Gpc^(-3). Adopting a
RL fraction 13.4+-3 per cent, this corresponds to rho = 12.5+-5.6 Gpc^(-3), in
good agreement with the SDSS QSO luminosity function in Fan et al. (2001). We
note the unusual QSO FIRST 1413+4505 (z=3.11), which shows strong associated
Lyalpha absorption and an extreme observed luminosity, L about 2 x 10^(15)
solar luminosities.Comment: Accepted for publication in MNRAS; 9 figures and 6 tables; Table 2 is
in landscape forma
The GAPS Programme with HARPS-N at TNG. X. Differential abundances in the XO-2 planet hosting binary
Binary stars hosting exoplanets are a unique laboratory where chemical
tagging can be performed to measure with high accuracy the elemental abundances
of both stellar components, with the aim to investigate the formation of
planets and their subsequent evolution. Here, we present a high-precision
differential abundance analysis of the XO-2 wide stellar binary based on high
resolution HARPS-N@TNG spectra. Both components are very similar K-dwarfs and
host planets. Since they formed presumably within the same molecular cloud, we
expect they should possess the same initial elemental abundances. We
investigate if the presence of planets can cause some chemical imprints in the
stellar atmospheric abundances. We measure abundances of 25 elements for both
stars with a range of condensation temperature K, achieving
typical precisions of dex. The North component shows abundances in
all elements higher by dex on average, with a mean
difference of +0.078 dex for elements with K. The
significance of the XO-2N abundance difference relative to XO-2S is at the
level for almost all elements. We discuss the possibility that this
result could be interpreted as the signature of the ingestion of material by
XO-2N or depletion in XO-2S due to locking of heavy elements by the planetary
companions. We estimate a mass of several tens of in heavy
elements. The difference in abundances between XO-2N and XO-2S shows a positive
correlation with the condensation temperatures of the elements, with a slope of
dex K, which could mean that both
components have not formed terrestrial planets, but that first experienced the
accretion of rocky core interior to the subsequent giant planets.Comment: 10 pages, 5 figures, accepted by Astronomy & Astrophysics. Numbering
of the series change
A galaxy overdensity at z=0.401 associated with an X-ray emitting structure of Warm-Hot Intergalactic Medium
We present the results of spectroscopic observations of galaxies associated
with the diffuse X-ray emitting structure discovered by Zappacosta et al.
(2002). After measuring the redshifts of 161 galaxies, we confirm an
overdensity of galaxies with projected dimensions of at least 2 Mpc, determine
its spectroscopic redshift in z=0.401+/-0.002, and show that it is spatially
coincident with the diffuse X-ray emission. This confirms the original claim
that this X-ray emission has an extragalactic nature and is due to the Warm-Hot
Intergalactic Medium (WHIM). We used this value of the redshift to compute the
temperature of the emitting gas. The resulting value depends on the metallicity
that is assumed for the IGM, and is constrained to be between 0.3 and 0.6 keV
for metallicities between 0.05 and 0.3 solar, in good agreement with the
expectations from the WHIM.Comment: 9 pages, A&A, in press, minor language change
The GAPS Programme with HARPS-N@TNG VI: The Curious Case of TrES-4b
We revisit the TrES-4 system parameters based on high-precision HARPS-N
radial-velocity measurements and new photometric light curves. A combined
spectroscopic and photometric analysis allows us to determine a spectroscopic
orbit with an amplitude m s. The derived mass of TrES-4b is
found to be , significantly lower than
previously reported. Combined with the large radius () inferred from our analysis, TrES-4b becomes
the second-lowest density transiting hot Jupiter known. We discuss several
scenarios to explain the puzzling discrepancy in the mass of TrES-4b in the
context of the exotic class of highly inflated transiting giant planets.Comment: 5 pages, 4 figures, Letter accepted for publication in Astronomy and
Astrophysic
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