84 research outputs found
New membership determination and proper motions of NGC 1817. Parametric and non-parametric approach
We have calculated proper motions and re-evaluated the membership
probabilities of 810 stars in the area of two NGC objects, NGC 1817 and NGC
1807. We have obtained absolute proper motions from 25 plates in the reference
system of the Tycho-2 Catalogue. The plates have a maximum epoch difference of
81 years; and they were taken with the double astrograph at Zo-Se station of
Shanghai Observatory, which has an aperture of 40 cm and a plate scale of 30
arcsec/mm. The average proper motion precision is 1.55 mas/yr. These proper
motions are used to determine the membership probabilities of stars in the
region, based on there being only one very extended physical cluster: NGC 1817.
With that aim, we have applied and compared parametric and non-parametric
approaches to cluster/field segregation. We have obtained a list of 169
probable member stars.Comment: 11 pages, 8 figures, A&A in pres
The extended halo of NGC 2682 (M 67) from Gaia DR2
Context: NGC 2682 is a nearby open cluster, approximately 3.5 Gyr old.
Dynamically, most open clusters should dissolve on shorter timescales, of ~ 1
Gyr. Having survived until now, NGC 2682 was likely much more massive in the
past, and is bound to have an interesting dynamical history. Aims: We
investigate the spatial distribution of NGC 2682 stars to constrain its
dynamical evolution, especially focusing on the marginally bound stars in the
cluster outskirts. Methods: We use Gaia DR2 data to identify NGC 2682 members
up to a distance of ~150 pc (10 degrees). Two methods (Clusterix and UPMASK)
are applied to this end. We estimate distances to obtain three-dimensional
stellar positions using a Bayesian approach to parallax inversion, with an
appropriate prior for star clusters. We calculate the orbit of NGC 2682 using
the GRAVPOT16 software. Results: The cluster extends up to 200 arcmin (50 pc)
which implies that its size is at least twice as previously believed. This
exceeds the cluster Hill sphere based on the Galactic potential at the distance
of NGC 2682. Conclusions: The extra-tidal stars in NGC 2682 may originate from
external perturbations such as disk shocking or dynamical evaporation from
two-body relaxation. The former origin is plausible given the orbit of NGC
2682, which crossed the Galactic disk ~40 Myr ago.Comment: 9 pages, 5 figures, accepted for publication on A&
The host of the Type I SLSN 2017egm: A young, sub-solar metallicity environment in a massive spiral galaxy
Here we present an integral-field study of the massive, high-metallicity
spiral NGC 3191, the host of SN 2017egm, the closest SLSN Type I to date. We
use data from PMAS/CAHA and the public MaNGA survey to shed light on the
properties of the SLSN site and the origin of star-formation in this
non-starburst spiral galaxy. We map the physical properties different
\ion{H}{II} regions throughout the galaxy and characterize their stellar
populations using the STARLIGHT fitting code. Kinematical information allows to
study a possible interaction with its neighbouring galaxy as the origin of
recent star formation activity which could have caused the SLSN. NGC 3191 shows
intense star-formation in the western part with three large SF regions of low
metallicity. The central regions of the host have a higher metallicity, lower
specific star-formation rate and lower ionization. Modeling the stellar
populations gives a different picture: The SLSN region has two dominant stellar
populations with different ages, the youngest one with an age of 2-10 Myr and
lower metallicity, likely the population from which the SN progenitor
originated. Emission line kinematics of NGC 3191 show indications of
interaction with its neighbour MCG+08-19-017 at 45 kpc, which might be
responsible for the recent starburst. In fact, this galaxy pair has in total
hosted 4 SNe, 1988B (Type Ia), SN 2003ds (Type Ic in MCG+08-19-017), PTF10bgl
(SLSN-Type II) and 2017egm, underlying the enhanced SF in both galaxies due to
interaction. Our study shows that one has to be careful interpreting global
host and even gas properties without looking at the stellar population history
of the region. SLSNe seem to still be consistent with massive stars ( 20
M) requiring low () metallicity and those environments
can also occur in massive, late-type galaxies but not necessarily starbursts.Comment: Accepted for publication in A&A, 13 pages, 11 figures, 7 tables.
Abstract has been reduced to match arXiv form requirement
uvby-Hbeta CCD photometry and membership segregation of the open cluster NGC 2548; Gaps in the Main Sequence of open clusters
Deep CCD photometry in the uvby-Hbeta intermediate-band system is presented
for the cluster NGC 2548 (M 48). A complete membership analysis based on
astrometric and photometric criteria is applied. The photometric analysis of a
selected sample of stars yields a reddening value of E(b-y)=0.06\pm0.03, a
distance modulus of V_0-M_V=9.3\pm0.5 (725 pc) and a metallicity of [Fe/H]=
-0.24\pm0.27. Through isochrone fitting we find an age of log t = 8.6\pm0.1
(400 Myr). Our optical photometry and JHK from 2MASS are combined to derive
effective temperatures of cluster member stars. The effective temperature
distribution along the main sequence of the cluster shows several gaps. A test
to study the significance of these gaps in the main sequence of the HR diagram
has been applied. The method is also applied to several other open clusters
(Pleiades, Hyades, NGC 1817 and M 67) to construct a sequence of metallicities
and ages. The comparison of the results of each cluster gives four gaps with
high significance (one of them, centred at 4900 K, has not been previously
reported).Comment: 11 pages, 8 figures, A&A in press. Corrected typos on Table
uvby-Hbeta CCD Photometry of NGC 1817 and NGC 1807
We have investigated the area of two NGC entries, NGC 1817 and NGC 1807, with
deep CCD photometry in the uvby-Hbeta intermediate-band system. The photometric
analysis of a selected sample of stars of the open cluster NGC 1817 yields a
reddening value of E(b-y)= 0.190.05, a distance modulus of V0-MV=
10.90.6, a metallicity of [Fe/H]= -0.340.26 and an age of log t =
9.050.05. Our measurements allow us to confirm that NGC 1807 is not a
physical cluster.Comment: 11 pages, 8 figures, A&A in pres
An All Sky Transmission Monitor: ASTMON
We present here the All Sky Transmission MONitor (ASTMON), designed to
perform a continuous monitoring of the surface brightness of the complete
night-sky in several bands. The data acquired are used to derive, in addition,
a subsequent map of the multiband atmospheric extinction at any location in the
sky, and a map of the cloud coverage. The instrument has been manufactured to
afford extreme weather conditions, and remain operative. Designed to be fully
robotic, it is ideal to be installed outdoors, as a permanent monitoring
station. The preliminary results based on two of the currently operative units
(at Do\~nana National Park - Huelva- and at the Calar Alto Observatory -
Almer\'ia -, in Spain), are presented here. The parameters derived using ASTMON
are in good agreement with previously reported ones, what illustrates the
validity of the design and the accuracy of the manufacturing. The information
provided by this instrument will be presented in forthcoming articles, once we
have accumulated a statistically amount of data.Comment: 12 Figures, Accepted for publishing in PAS
A study of the neglected Galactic HII region NGC 2579 and its companion ESO 370-9
The Galactic HII region NGC 2579 has stayed undeservedly unexplored due to
identification problems which persisted until recently. Both NGC 2579 and its
companion ESO 370-9 have been misclassified as planetary or reflection nebula,
confused with each other and with other objects. Due to its high surface
brightness, high excitation, angular size of few arcminutes and relatively low
interstellar extinction, NGC 2579 is an ideal object for investigations in the
optical range. Located in the outer Galaxy, NGC 2579 is an excellent object for
studying the Galactic chemical abundance gradients. In this paper we present
the first comprehensive observational study on the nebular and stellar
properties of NGC 2579 and ESO 370-9, including the determination of electron
temperature, density structure, chemical composition, kinematics, distance, and
the identification and spectral classification of the ionizing stars, and
discuss the nature of ESO 370-9. Long slit spectrophotometric data in the
optical range were used to derive the nebular electron temperature, density and
chemical abundances and for the spectral classification of the ionizing star
candidates. Halpha and UBV CCD photometry was carried out to derive stellar
distances from spectroscopic parallax and to measure the ionizing photon flux.Comment: To be published in Astronomy & Astrophysic
The CARMENES search for exoplanets around M dwarfs: Nine new double-line spectroscopic binary stars
Context. The CARMENES spectrograph is surveying ~300 M dwarf stars in search
for exoplanets. Among the target stars, spectroscopic binary systems have been
discovered, which can be used to measure fundamental properties of stars. Aims.
Using spectroscopic observations, we determine the orbital and physical
properties of nine new double-line spectroscopic binary systems by analysing
their radial velocity curves. Methods. We use two-dimensional cross-correlation
techniques to derive the radial velocities of the targets, which are then
employed to determine the orbital properties. Photometric data from the
literature are also analysed to search for possible eclipses and to measure
stellar variability, which can yield rotation periods. Results. Out of the 342
stars selected for the CARMENES survey, 9 have been found to be double-line
spectroscopic binaries, with periods ranging from 1.13 to ~8000 days and orbits
with eccentricities up to 0.54. We provide empirical orbital properties and
minimum masses for the sample of spectroscopic binaries. Absolute masses are
also estimated from mass-luminosity calibrations, ranging between ~0.1 and ~0.6
Msol . Conclusions. These new binary systems increase the number of double-line
M dwarf binary systems with known orbital parameters by 15%, and they have
lower mass ratios on average.Comment: Accepted for publication in A&A. 17 pages, 4 figure
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