37 research outputs found
Towards a calibration of SSP models from the optical to the mid-infrared
Our knowledge about unresolved stellar systems comes from comparing
integrated-light properties to SSP models. Therefore it is crucial to calibrate
the latter as well as possible by integrated-light colors of clusters that have
reliable ages and metallicities (deep CMDs and/or spectroscopy of individual
giants). This is especially true for the NIR and MIR, which contain important
population synthesis diagnostics and are often used to derive masses of stellar
systems at hight redshifts. Here we present integrated colors of MC clusters
using new VRI photometry and 2MASS data. In the imminent future we will include
MIR data from Spitzer/IRAC. We compare our new colors with popular SSP models
to illustrate their strengths and weaknesses.Comment: 2 pages, 1 figure, to appear in the proceedings of IAU Symposium
No241 "Stellar Populations as building blocks of galaxies", A. Vazdekis & R.
Peletier, ed
Haffner 16: A Young Moving Group in the Making
The photometric properties of main sequence (MS) and pre-main sequence (PMS)
stars in the young cluster Haffner 16 are examined using images recorded with
the Gemini South Adaptive Optics Imager (GSAOI) and corrected for atmospheric
blurring by the Gemini Multi-Conjugate Adapative Optics System (GeMS). A rich
population of PMS stars is identified, and comparisons with isochrones suggest
an age < 10 Myr assuming a distance modulus of 13.5 (D = 5 kpc). When compared
with the solar neighborhood, Haffner 16 is roughly a factor of two deficient in
objects with sub-solar masses. PMS objects in the cluster are also more
uniformly distributed on the sky than bright MS stars. It is suggested that
Haffner 16 is dynamically evolved, and that it is shedding protostars with
sub-solar masses. Young low mass clusters like Haffner 16 are one possible
source of PMS stars in the field. The cluster will probably evolve on time
scales of ~ 100 - 1000 Myr into a diffuse moving group with a mass function
that is very different from that which prevailed early in its life.Comment: To appear in the Publications of the Astronomical Society of the
Pacifi
Discovery of New Milky Way Star Clusters Candidates in the 2MASS Point Source Catalog
A systematic search of the 2MASS point source catalog, covering 47% of the
sky, was carried out aiming to reveal any hidden globular clusters in our
Galaxy. Eight new star clusters were discovered by a search algorithm based on
finding peaks in the apparent stellar surface density, and a visual inspection
of their vicinities yielded additional two. They all are concentrated toward
the Galactic plane and are hidden behind up to Av=20 mag which accounts for
their late discovery. The majority of new clusters are associated with H II
regions or unidentified IRAS sources suggesting that they are young, probably
similar to Arches or open clusters. Only one candidate has morphology similar
to a globular cluster and the verification of its nature will require deeper
observations with higher angular resolution than the 2MASS data.Comment: 4 pages, 3 figures (1 is a jpeg file), acccepted for publication in
Astronomy and Astrophysic
On the distribution of initial masses of stellar clusters inferred from synthesis models
The fundamental properties of stellar clusters, such as the age or the total
initial mass in stars, are often inferred from population synthesis models. The
predicted properties are then used to constrain the physical mechanisms
involved in the formation of such clusters in a variety of environments.
Population synthesis models cannot, however, be applied blindy to such systems.
We show that synthesis models cannot be used in the usual straightforward way
to small-mass clusters (say, M < few times 10**4 Mo). The reason is that the
basic hypothesis underlying population synthesis (a fixed proportionality
between the number of stars in the different evolutionary phases) is not
fulfilled in these clusters due to their small number of stars. This incomplete
sampling of the stellar mass function results in a non-gaussian distribution of
the mass-luminosity ratio for clusters that share the same evolutionary
conditions (age, metallicity and initial stellar mass distribution function).
We review some tests that can be carried out a priori to check whether a given
cluster can be analysed with the fully-sampled standard population synthesis
models, or, on the contrary, a probabilistic framework must be used. This leads
to a re-assessment in the estimation of the low-mass tail in the distribution
function of initial masses of stellar clusters.Comment: 5 pages, 1 figure, to appear in ``Young Massive Star Clusters -
Initial Conditions and Environments'', 2008, Astrophysics & Space Science,
eds. E. Perez, R. de Grijs, R. M. Gonzalez Delgad
The January 2015 outburst of a red nova in M31
M31N 2015-01a (or M31LRN 2015) is a red nova that erupted in January 2015 --
the first event of this kind observed in M31 since 1988. Very few similar
events have been confirmed as of 2015. Most of them are considered to be
products of stellar mergers. Results of an extensive optical monitoring of the
transient in the period January-March 2015 are presented. Eight optical
telescopes were used for imaging. Spectra were obtained on BTA, GTC and the
Rozhen 2m telescope. We present a highly accurate 70 d lightcurve and
astrometry with a 0.05" uncertainty. The color indices reached a minimum 2-3 d
before peak brightness and rapidly increased afterwards. The spectral type
changed from F5I to F0I in 6 d before the maximum and then to K3I in the next
30 d. The luminosity of the transient was estimated to
during the optical maximum. Both the
photometric and the spectroscopic results confirm that the object is a red
nova, similar to V838 Monocerotis.Comment: 5 pages, 4 figures, 4 tables, accepted for publication in Astronomy
and Astrophysics as a Letter to the Editor; page 5 is online material onl
Discovery of New Milky Way Star Cluster Candidates in the 2MASS Point Source Catalog II. Physical Properties of the Star Cluster CC01
Three new obscured Milky Way clusters were detected as surface density peaks
in the 2MASS point source catalog during our on-going search for hidden
globular clusters and massive Arches-like star clusters. One more cluster was
discovered serendipitously during a visual inspection of the candidates.
The first deep J, H, and Ks imaging of the cluster [IBP2002] CC01 is
presented. We estimated a cluster age of ~1-3 Myr, distance modulus of
(m-M)0=12.56+-0.08 mag (D=3.5 Kpc), and extinction of AV~7.7 mag. We also
derived the initial mass function slope for the cluster: Gamma=-2.23+-0.16. The
integration over the initial mass function yielded a total cluster mass
M_{total}<=1800+-200Msol. CC01 appears to be a regular, not very massive star
cluster, whose formation has probably been induced by the shock front from the
nearby HII region Sh2-228.Comment: 8 pages, 9 figures, accepted in A&
AT 2019abn: multi-wavelength observations of the first 200 days
AT 2019abn was discovered in the nearby M51 galaxy, by the Zwicky Transient Facility more than two magnitudes, and around 3 weeks, prior to its optical peak. We aimed to conduct a detailed photometric and spectroscopic follow-up campaign for AT 2019abn, with the early discovery allowing significant pre-maximum observations of an intermediate luminosity red transient (ILRT) for the first time. This work is based around the analysis of u'BVr'i'z'H photometry and low-resolution spectroscopy with the Liverpool Telescope, medium-resolution spectroscopy with Gran Telescopio Canarias (GTC) and near-infrared imaging with GTC and the Nordic Optical Telescope. We present the most detailed optical light curve of an ILRT to date, with multi-band photometry starting around three weeks before peak brightness. The transient peaked at an observed absolute magnitude of M_r=-13.1, although it is subject to significant reddening from dust in M51, implying an intrinsic M_r~-15.2. The initial light curve showed a linear, achromatic rise in magnitude, before becoming bluer at peak. After peak brightness the transient gradually cooled. This is reflected in our spectra which at later times show absorption from species such as Fe I, Ni I and Li I. A spectrum taken around peak brightness shows narrow, low-velocity absorption lines, which we interpret as likely originating from pre-existing circumstellar material. We conclude that, while there are some peculiarities, such as the radius evolution, AT 2019abn overall fits in well with the ILRT class of objects, and is the most luminous member of the class seen to date
AT 2019abn:multi-wavelength observations of the first 200 days
AT 2019abn was discovered in the nearby M51 galaxy, by the Zwicky Transient Facility more than two magnitudes, and around 3 weeks, prior to its optical peak. We aimed to conduct a detailed photometric and spectroscopic follow-up campaign for AT 2019abn, with the early discovery allowing significant pre-maximum observations of an intermediate luminosity red transient (ILRT) for the first time. This work is based around the analysis of u'BVr'i'z'H photometry and low-resolution spectroscopy with the Liverpool Telescope, medium-resolution spectroscopy with Gran Telescopio Canarias (GTC) and near-infrared imaging with GTC and the Nordic Optical Telescope. We present the most detailed optical light curve of an ILRT to date, with multi-band photometry starting around three weeks before peak brightness. The transient peaked at an observed absolute magnitude of M_r=-13.1, although it is subject to significant reddening from dust in M51, implying an intrinsic M_r~-15.2. The initial light curve showed a linear, achromatic rise in magnitude, before becoming bluer at peak. After peak brightness the transient gradually cooled. This is reflected in our spectra which at later times show absorption from species such as Fe I, Ni I and Li I. A spectrum taken around peak brightness shows narrow, low-velocity absorption lines, which we interpret as likely originating from pre-existing circumstellar material. We conclude that, while there are some peculiarities, such as the radius evolution, AT 2019abn overall fits in well with the ILRT class of objects, and is the most luminous member of the class seen to date
The January 2015 outburst of a red nova in M 31
Context. M31N 2015-01a (or M31LRN 2015) is a red nova that erupted in January 2015 – the first event of this kind observed in M31 since 1988. Very few similar events have been confirmed as of 2015. Most of them are considered to be products of stellar mergers.Aims. Results of an extensive optical monitoring of the transient in the period January-March 2015 are presented.Methods. Eight optical telescopes were used for imaging. Spectra were obtained on BTA, GTC and the Rozhen 2m telescope.Results. We present a highly accurate 70 d lightcurve and astrometry with a 0.05′′uncertainty. The color indices reached a minimum 2-3 d before peak brightness and rapidly increased afterwards. The spectral type changed from F5I to F0I in 6 d before the maximum and then to K3I in the next 30 d. The luminosity of the transient was estimated to 8.7+3.3 −2.2 × 105 L⊙ during the optical maximum.Conclusions. Both the photometric and the spectroscopic results confirm that the object is a red nova, similar to V838 Monocerotis
Discovery of new Milky Way star cluster candidates in the 2MASS Point Source Catalog IV. Follow-up observations of cluster candidates in the Galactic plane
Nearly 500 cluster candidates have been reported by searches based on the new
all-sky near infrared surveys. The true nature of the majority of these objects
is still unknown. This project aims to estimate the physical parameters of some
of the candidates in order to use them as probes of the obscured star formation
in the Milky Way.
Here we report deep near infrared observations of four objects, discovered by
our search based on the 2MASS Point Source Catalog (Ivanov et al. 2002;
Borissova et al. 2003). CC04 appears to be a few million year old cluster. We
estimate its distance and extinction, and set a limit on the total mass. CC08
contains red supergiants, indicating a slightly older age of about 7-10 Myr.
The suspected cluster nature of CC13 was not confirmed. CC14 appears to be an
interesting candidate with double-tail-like morphology but our data doesn't
allow us to derive a firm conclusion about the nature of this object.
We found no supermassive star clusters similar to the Arches or the
Quintuplet (Mtot >= 10**4 Msolar) among the dozen confirmed clusters studied so
far in this series of papers, indicating that such objects are not common in
the Milky Way.Comment: 6 pages, 8 pages; accepted for publication in Astronomy and
Astrophysic