60 research outputs found
The Araucaria Project. An improved distance to the Sculptor spiral galaxy NGC 300 from its Cepheid variables
In a previous paper, we reported on the discovery of more than a hundred new
Cepheid variables in the Sculptor Group spiral NGC 300 from wide-field images
taken in the B and V photometric bands at ESO/La Silla. In this paper, we
present additional VI data, derive improved periods and mean magnitudes for the
variables, and construct period-luminosity relations in the V, I and the
reddening-independent (V-I) Wesenheit bands using 58 Cepheid variables with
periods between 11 and 90 days. We obtain tightly defined relations, and by
fitting the slopes determined for the LMC Cepheids by the OGLE II Project we
obtain reddening-corrected distances to the galaxy in all bands. We adopt as
our best value the distance derived from the reddening-free Wesenheit
magnitudes, which is 26.43 0.04 (random) 0.05 (systematic) mag. We
argue that our current distance result for NGC 300 is the most accurate which
has so far been obtained using Cepheid variables, and that it is largely free
from systematic effects due to metallicity, blending, and sample selection. It
agrees very well with the recent distance determination from the tip of the red
giant branch method obtained from HST data by Butler et al. (2004), and it is
consistent with the Cepheid distance to NGC 300 which was derived by Freedman
et al. (2001) from CCD photometry of a smaller sample of stars.Comment: Latex, Astronomical Journal in pres
The EFIGI catalogue of 4458 nearby galaxies with detailed morphology
Accepted for publication in Astronomy and Astrophysics, 27 pages, 7 tables, 32 colour figures. Data available at http://www.efigi.orgInternational audienceNow that large databases of resolved galaxy images are provided by modern imaging surveys, advanced morphological studies can be envisioned, urging for well defined calibration samples. We present the EFIGI catalogue, a multiwavelength database specifically designed for a dense sampling of all Hubble types. The catalogue merges data from standard surveys and catalogues (Principal Galaxy Catalogue, Sloan Digital Sky Survey, Value-Added Galaxy Catalogue, HyperLeda, and the NASA Extragalactic Database) and provides detailed morphological information. Imaging data are obtained from the SDSS DR4 in the u, g, r, i, and z bands for a sample of 4458 PGC galaxies, whereas photometric and spectroscopic data are obtained from the SDSS DR5 catalogue. Point-Spread Function models are derived in all five bands. Composite colour images of all objects are visually examined by a group of astronomers, and galaxies are staged along the Hubble sequence and classified according to 16 morphological attributes describing their structure, texture, as well as environment and appearance on a five-level scale. The EFIGI Hubble sequence shows remarkable agreement with the RC3 Revised Hubble Sequence. The main characteristics and reliability of the catalogue are examined, including photometric completeness, type mix, systematic trends and correlations. The final EFIGI database is a large sub-sample of the local Universe, with a dense sampling of Sd, Sdm, Sm and Im types compared to magnitude-limited catalogues. We estimate the photometric catalogue to be more than ~ 80% complete for galaxies with 10 < g < 14. More than 99.5% of EFIGI galaxies have a known redshift in the HyperLeda and NED databases
The Araucaria Project. First Cepheid Distance to the Sculptor Group Galaxy NGC 7793 from Variables discovered in a Wide-Field Imaging Survey
We have detected, for the first time, Cepheid variables in the Sculptor Group
spiral galaxy NGC 7793. From wide-field images obtained in the optical V and I
bands on 56 nights in 2003-2005, we have discovered 17 long-period (24-62 days)
Cepheids whose periods and mean magnitudes define tight period-luminosity
relations. We use the (V-I) Wesenheit index to determine a reddening-free true
distance modulus to NGC 7793 of 27.68 +- 0.05 mag (internal error) +- 0.08 mag
(systematic error). The comparison of the reddened distance moduli in V and I
with the one derived from the Wesenheit magnitude indicates that the Cepheids
in NGC 7793 are affected by an average total reddening of E(B-V)=0.08 mag, 0.06
of which is produced inside the host galaxy. As in the earlier Cepheid studies
of the Araucaria Project, the reported distance is tied to an assumed LMC
distance modulus of 18.50. The quoted systematic uncertainty takes into account
effects like blending and possible inhomogeneous filling of the Cepheid
instability strip on the derived distance. The reported distance value does not
depend on the (unknown) metallicity of the Cepheids according to recent
theoretical and empirical results. Our Cepheid distance is shorter, but within
the errors consistent with the distance to NGC 7793 determined earlier with the
TRGB and Tully-Fisher methods. The NGC 7793 distance of 3.4 Mpc is almost
identical to the one our project had found from Cepheid variables for NGC 247,
another spiral member of the Sculptor Group located close to NGC 7793 on the
sky. Two other conspicuous spiral galaxies in the Sculptor Group, NGC 55 and
NGC 300, are much nearer (1.9 Mpc), confirming the picture of a very elongated
structure of the Sculptor Group in the line of sight put forward by Jerjen et
al. and others.Comment: AJ in pres
APERO: A PipelinE to Reduce Observations -- Demonstration with SPIRou
With the maturation of near-infrared high-resolution spectroscopy, especially
when used for precision radial velocity, data reduction has faced unprecedented
challenges in terms of how one goes from raw data to calibrated, extracted, and
corrected data with required precisions of thousandths of a pixel. Here we
present APERO (A PipelinE to Reduce Observations), specifically focused on
SPIRou, the near-infrared spectropolarimeter on the Canada--France--Hawaii
Telescope (SPectropolarim\`etre InfraROUge, CFHT). In this paper, we give an
overview of APERO and detail the reduction procedure for SPIRou. APERO delivers
telluric-corrected 2D and 1D spectra as well as polarimetry products. APERO
enables precise stable radial velocity measurements on sky (via the LBL
algorithm), good to at least ~2 m/s over the current 5-year lifetime of SPIRou.Comment: Accepted for publication in PASP. 55 pages, 29 figures, 10 pages of
Appendice
Comprehensive High-resolution Chemical Spectroscopy of Barnard's Star with SPIRou
Determination of fundamental parameters of stars impacts all fields of
astrophysics, from galaxy evolution to constraining the internal structure of
exoplanets. This paper presents a detailed spectroscopic analysis of Barnard's
star that compares an exceptionally high-quality (signal-to-noise ratio of
2500 in the band), high-resolution NIR spectrum taken with CFHT/SPIRou
to PHOENIX-ACES stellar atmosphere models. The observed spectrum shows
thousands of lines not identified in the models with a similar large number of
lines present in the model but not in the observed data. We also identify
several other caveats such as continuum mismatch, unresolved contamination and
spectral lines significantly shifted from their expected wavelengths, all of
these can be a source of bias for abundance determination. Out of
observed lines in the NIR that could be used for chemical spectroscopy, we
identify a short list of a few hundred lines that are reliable. We present a
novel method for determining the effective temperature and overall metallicity
of slowly-rotating M dwarfs that uses several groups of lines as opposed to
bulk spectral fitting methods. With this method, we infer = 3231
21 K for Barnard's star, consistent with the value of 3238 11 K
inferred from the interferometric method. We also provide abundance
measurements of 15 different elements for Barnard's star, including the
abundances of four elements (K, O, Y, Th) never reported before for this star.
This work emphasizes the need to improve current atmosphere models to fully
exploit the NIR domain for chemical spectroscopy analysis.Comment: 24 pages, 18 figures, submitted to Ap
Reddening and Extinction Toward the Galactic Bulge from OGLE-III: The Inner Milky Way's Rv ~ 2.5 Extinction Curve
We combine VI photometry from OGLE-III with VVV and 2MASS measurements of
E(J-K_{s}) to resolve the longstanding problem of the non-standard optical
extinction toward the Galactic bulge. We show that the extinction is well-fit
by the relation A_{I} = 0.7465*E(V-I) + 1.3700*E(J-K_{s}), or, equivalently,
A_{I} = 1.217*E(V-I)(1+1.126*(E(J-K_{s})/E(V-I)-0.3433)). The optical and
near-IR reddening law toward the inner Galaxy approximately follows an R_{V}
\approx 2.5 extinction curve with a dispersion {\sigma}_{R_{V}} \approx 0.2,
consistent with extragalactic investigations of the hosts of type Ia SNe.
Differential reddening is shown to be significant on scales as small as as our
mean field size of 6', with the 1{\sigma} dispersion in reddening averaging 9%
of total reddening for our fields. The intrinsic luminosity parameters of the
Galactic bulge red clump (RC) are derived to be (M_{I,RC}, \sigma_{I,RC,0},
(V-I)_{RC,0}, \sigma_{(V-I)_{RC}}, (J-K_{s})_{RC,0}) = (-0.12, 0.09, 1.06,
0.121, 0.66). Our measurements of the RC brightness, brightness dispersion and
number counts allow us to estimate several Galactic bulge structural
parameters. We estimate a distance to the Galactic center of 8.20 kpc,
resolving previous discrepancies in distance determinations to the bulge based
on I-band observations. We measure an upper bound on the tilt {\alpha} \approx
40{\deg}. between the bar's major axis and the Sun-Galactic center line of
sight, though our brightness peaks are consistent with predictions of an N-body
model oriented at {\alpha} \approx 25{\deg}. The number of RC stars suggests a
total stellar mass for the Galactic bulge of 2.0*10^{10} M_{\odot}, if one
assumes a Salpeter IMF.Comment: 61 Pages, 21 Figures, 4 Tables, Submitted to The Astrophysical
Journal and modified as per a referee report. Includes reddening, reddening
law, differential reddening, mean distance, dispersion in distance, surface
density of stars and errors thereof for ~9,000 bulge sightlines. For a brief
video explaining the key result of this paper, see
http://www.youtube.com/user/OSUAstronom
Parallax of OGLE-2018-BLG-0596: A Low-mass-ratio Planet around an M-dwarf
We report the discovery of a microlensing planet
OGLE-2018-BLG-0596Lb, with preferred planet-host mass ratio . The planetary signal, which is characterized by a short "bump" on the rising side of the lensing light curve, was densely
covered by ground-based surveys. We find that the signal can be explained by a
bright source that fully envelops the planetary caustic, i.e., a "Hollywood"
geometry. Combined with the source proper motion measured from , the
satellite parallax measurement makes it possible to precisely
constrain the lens physical parameters. The preferred solution, in which the
planet perturbs the minor image due to lensing by the host, yields a
Uranus-mass planet with a mass of orbiting
a mid M-dwarf with a mass of . There is also
a second possible solution that is substantially disfavored but cannot be ruled
out, for which the planet perturbs the major image. The latter solution yields
and . By
combining the microlensing and data together with a Galactic model, we
find in either case that the lens lies on the near side of the Galactic bulge
at a distance . Future adaptive optics
observations may decisively resolve the major image/minor image degeneracy.Comment: 34 pages, 8 figures, Submitted to AAS journa
CO or no CO? Narrowing the CO abundance constraint and recovering the H2O detection in the atmosphere of WASP-127 b using SPIRou
Precise measurements of chemical abundances in planetary atmospheres are
necessary to constrain the formation histories of exoplanets. A recent study of
WASP-127b, a close-in puffy sub-Saturn orbiting its solar-type host star in 4.2
d, using HST and Spitzer revealed a feature-rich transmission spectrum with
strong excess absorption at 4.5 um. However, the limited spectral resolution
and coverage of these instruments could not distinguish between CO and/or CO2
absorption causing this signal, with both low and high C/O ratio scenarios
being possible. Here we present near-infrared (0.9--2.5 um) transit
observations of WASP-127 b using the high-resolution SPIRou spectrograph, with
the goal to disentangle CO from CO2 through the 2.3 um CO band. With SPIRou, we
detect H2O at a t-test significance of 5.3 sigma and observe a tentative (3
sigma) signal consistent with OH absorption. From a joint SPIRou + HST +
Spitzer retrieval analysis, we rule out a CO-rich scenario by placing an upper
limit on the CO abundance of log10[CO]<-4.0, and estimate a log10[CO2] of
-3.7^(+0.8)_(-0.6), which is the level needed to match the excess absorption
seen at 4.5um. We also set abundance constraints on other major C-, O-, and
N-bearing molecules, with our results favoring low C/O (0.10^(+0.10)_(-0.06)),
disequilibrium chemistry scenarios. We further discuss the implications of our
results in the context of planet formation. Additional observations at high and
low-resolution will be needed to confirm these results and better our
understanding of this unusual world.Comment: 23 pages, 13 figures, Submitted for publication in the Monthly Notice
of the Royal Astronomical Societ
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