542 research outputs found
Synthetic extinction maps around intermediate-mass black holes in Galactic globular clusters
During the last decades, much effort has been devoted to explain the
discrepancy between the amount of intracluster medium (ICM) estimated from
stellar evolution theories and that emerging from observations in globular
clusters (GCs). One possible scenario is the accretion of this medium by an
intermediate-mass black hole (IMBH) at the centre of the cluster. In this work,
we aim at modelling the cluster colour-excess profile as a tracer of the ICM
density, both with and without an IMBH. Comparing the profiles with
observations allows us to test the existence of IMBHs and their possible role
in the cleansing of the ICM. We derive the intracluster density profiles from
hydrodynamical models of accretion onto a central IMBH in a GC and we determine
the corresponding dust density. This model is applied to a list of 25 Galactic
GCs. We find that central IMBHs decrease the ICM by several orders of
magnitude. In a subset of 9 clusters, the absence of the black hole combined
with a low intracluster medium temperature would be at odds with present gas
mass content estimations. As a result, we conclude that IMBHs are an effective
cleansing mechanism of the ICM of GCs. We construct synthetic extinction maps
for M 62 and {\omega} Cen, two clusters in the small subset of 9 with observed
2D extinction maps. We find that under reasonable assumptions regarding the
model parameters, if the gas temperature in M 62 is close to 8000 K, an IMBH
needs to be invoked. Further ICM observations regarding both the gas and dust
in GCs could help to settle this issue.Comment: Accepted for publication in MNRAS.11 pages, 7 figure
Extinction ratios in the inner Galaxy as revealed by the VVV survey
Accepted for publication in ApJ Letters, 10 pages, 3 Figures, 2 Tables © 2017 The American Astronomical Society. All rights reserved.Interstellar extinction towards the Galactic Center is large and significantly differential. Its reddening and dimming effects in red clump stars in the Galactic Bulge can be exploited to better constrain the extinction law towards the innermost Galaxy. By virtue of a deep and complete catalog of more than 30 million objets at and obtained from VVV survey observations, we apply the red clump method to infer the selective-to-total extinction ratios in the , , , and broadband near-infrared filters. The measured values are smaller than previously reported, and are not constant, with mean values, e.g., and . We also obtain a ratio :::: of 7.74:5.38:3.30:1.88:1.0, implying extinction towards the Galactic Center to follow a distribution as a function of wavelength steeper than previously reported, consistent with a power law in the near-infrared.Peer reviewedFinal Accepted Versio
Confirmation of a New Metal-poor Globular Cluster in the Galactic Bulge
© 2018. The American Astronomical Society. All rights reserved.We use deep near-IR photometry of the VISTA Variables in the V'a L'ctea (VVV) Survey and deep DECam Plane Survey (DECaPS) optical photometry to confirm the physical reality of the candidate globular cluster (GC) Minni 22, which is located in the Galactic bulge. This object, which was detected as a high density region in our maps of bulge red giants, is now confirmed as a real GC based on the optical and near-IR color'magnitude diagrams. We also recover three known fundamental mode (ab type) RR Lyrae stars within 2 arcmin of the cluster center. The presence of RR Lyrae stars also seems to confirm Minni 22 as a bonafide old and metal-poor GC. We estimate a cluster reddening E(J - Ks) = 0.6 mag and determine its heliocentric distance D = 7.4 ± 0.3 kpc. The optical and near-IR color'magnitude diagrams reveal well-defined red giant branches in all cases, including a red giant branch bump at Ks = 13.30 ± 0.05 mag. The comparison with theoretical isochrones yields a mean metallicity of [Fe/H] = -1.3 ± 0.3 dex, and age of t ∼ 11.2 Gyr. This is a good example of a new low-luminosity (MV = -6.2 mag) GC found in the central bulge of the Milky Way. After discussing the different ways to confirm the existence of bulge GC candidates, we find that one of the best methods is to use the CMDs from the combination of the DECaPS + VVV photometries.Peer reviewe
An analysis of the composite stellar population in M32
We obtained long-slit spectra of high signal-to-noise ratio of the galaxy M32
with the GMOS spectrograph at the GEMINI North telescope. We analysed the
integrated spectra by means of full spectral fitting in order to extract the
mixture of stellar populations that best represents its composite nature. Three
different galactic radii were analysed, from the nuclear region out to 2 arcmin
from the centre. This allows us to compare, for the first time, the results of
integrated light spectroscopy with those of resolved colour-magnitude diagrams
from the literature. As our main result, we propose that an ancient and an
intermediate-age population coexist in M32, and that the balance between these
two populations change between the nucleus and outside 1 effective radius in
the sense that the contribution from the intermediate population is larger at
the nuclear region. We retrieve a smaller signal of a young population at all
radii whose origin is unclear and may be a contamination from horizontal-branch
stars, such as the ones identified by Brown et al. in the nuclear region. We
compare our metallicity distribution function for a region 1 to 2 arcmin from
the centre to the one obtained with photometric data by Grillmair et al. Both
distributions are broad, but our spectroscopically derived distribution has a
significant component with [Z/Z_{\sun}] \leq -1, which is not found by
Grillmair et al.Comment: accepted for publication in MNRA
The VVV-SkZ pipeline: an automatic PSF-fitting photometric pipeline for the VVV survey
We present the VVV-SkZ_pipeline, a DAOPHOT-based photometric pipeline,
created to perform PSF-fitting photometry of "VISTA Variables in the V\'ia
L\'actea" (VVV) ESO Public Survey data. The pipeline replaces the user avoiding
repetitive interaction in all the operations, retaining all of the benefits of
the power and accuracy of the DAOPHOT suite. The pipeline provides an
astrometrized photometric catalog reliable up to more than 2 magnitudes
brighter than the saturation limit, where other techniques fail. It also
produces deeper and more accurate photometry. These achievements allow the
VVV-SkZ_pipeline to produce data well anchored to the selected standard
photometric system and analyze important phenomena (i.e. TRGB, RGB slope, HB
morphology, RR Lyrae), that other methods are not able to manage.Comment: Accepted by RevMexAA for vol. 49, n.2, October 201
Open cluster candidates in the VVVX area: VVVX CL 076 and CL 077
We are reporting some basic parameters of two newly discovered clusters, VVVX CL 076 and CL 077, recently discovered in the galactic disk area covered by the VISTA Variables in the Via Lactea eXtended (VVVX) ESO Public Survey. The preliminary analysis shows that both clusters are young and relatively close to the Sun.Peer reviewedFinal Published versio
- …