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Sharina M.,Russian Academy of Sciences | Aringer B.,University of Vienna | Davoust E.,French National Center for Scientific Research | Kniazev A.Y.,South African Astronomical Observatory | And 3 more authors.
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

We report on the serendipitous discovery of a carbon star near the centre of the low-metallicity globular cluster NGC 6426. We determined its membership and chemical properties using medium-resolution spectra. The radial velocity of -159 km s-1 makes it a member of the cluster. We used photometric data from the literature and the COMARCS stellar atmospheric models to derive its luminosity, effective temperature, surface gravity, metallicity, and approximate C, N and O abundance ratios. According to these properties, we suggest that this star is a genuine carbon-rich low-metallicity asymptotic giant branch star. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS. Source


Madrid J.P.,Swinburne University of Technology | Donzelli C.J.,Institute Investigaciones en Astronomia Teorica y Experimental IATE | Donzelli C.J.,CONICET
Astrophysical Journal | Year: 2013

A spectroscopic follow-up of ultracompact dwarf (UCD) candidates in the fossil group NGC 1132 is undertaken with the Gemini Multi Object Spectrograph. These new Gemini spectra prove the presence of six UCDs in the fossil group NGC 1132 at a distance of D ∼ 100 Mpc and a recessional velocity of vr = 6935 ± 11 km s-1. The brightest and largest member of the UCD population is an M32 analog with a size of 77.1 pc and a magnitude of MV = -14.8 mag with the characteristics in between those of the brightest UCDs and compact elliptical galaxies. The ensemble of UCDs have an average radial velocity of 〈vr 〉 = 6966 ± 208 km s-1 and a velocity dispersion of σ v = 169 ± 18 km s-1 similar to the one of poor galaxy groups. This work shows that UCDs can be used as test particles to determine the dynamical properties of galaxy groups. The presence of UCDs in the fossil group environment is confirmed and thus the fact that UCDs can form across diverse evolutionary conditions. © 2013. The American Astronomical Society. All rights reserved.. Source


Davoust E.,French National Center for Scientific Research | Sharina M.E.,French National Center for Scientific Research | Sharina M.E.,Russian Academy of Sciences | Donzelli C.J.,Institute Investigaciones en Astronomia Teorica y Experimental IATE | Donzelli C.J.,CONICET
Astronomy and Astrophysics | Year: 2011

Context. First classified as an open cluster, BH 176 lies in a crowded field at low galactic latitude. Later studies have labeled it a transition-type object, a metal-rich globular, or an open cluster, with distance estimates in the range of 15 to 85 kpc, indicating that the true nature of this cluster is rather uncertain. Aims. Our aim is to determine more precisely the distance to BH 176, and, as a matter of consequence, its metallicity and age. Methods. We have obtained two color-magnitude diagrams of BH 176, one in the infrared using the 2MASS point-source catalog, the other in the optical using FORS2 VLT archival images. We identified the red giant branch in the infrared and the red giant branch, red giant bump, red horizontal branch, subgiant branch, and main sequence turn-off in the optical, by selecting stars within ∼2-3′ from the center of the cluster. Results. We estimate a distance D ∼15.1 ± 0.5 kpc from the visual magnitude of the red clump and a metallicity [Fe/H] ∼-0.10 ± 0.1 dex from the magnitudes and colors of the main features in the two color-magnitude diagrams. Fitting isochrones from the Padova database to the color-magnitude diagrams confirms our results. Conclusions. BH 176 is an old metal-rich open or transition-type cluster, moderately close to the Galactic plane. It is a spectacular object for studying the early formation history of our Galaxy. © 2011 ESO. Source


Donzelli C.J.,Institute Investigaciones en Astronomia Teorica y Experimental IATE | Donzelli C.J.,CONICET | Muriel H.,Institute Investigaciones en Astronomia Teorica y Experimental IATE | Muriel H.,CONICET | Madrid J.P.,Swinburne University of Technology
Astrophysical Journal, Supplement Series | Year: 2011

We have derived detailed R-band luminosity profiles and structural parameters for a total of 430 brightest cluster galaxies (BCGs), down to a limiting surface brightness of 24.5magarcsec-2. Light profiles were initially fitted with a Sérsic's R 1/n model, but we found that 205 (∼48%) BCGs require a double component model to accurately match their light profiles. The best fit for these 205 galaxies is an inner Sérsic model, with indices n 1-7, plus an outer exponential component. Thus, we establish the existence of two categories of the BCG luminosity profiles: single and double component profiles. We found that double profile BCGs are brighter (∼0.2mag) than single profile BCGs. In fact, the Kolmogorov-Smirnov test applied to these subsamples indicates that they have different total magnitude distributions, with mean values MR = -23.8 ± 0.6mag for single profile BCGs and MR = -24.0 ± 0.5mag for double profile BCGs. We find that partial luminosities for both subsamples are indistinguishable up to r = 15kpc, while for r > 20kpc the luminosities we obtain are on average 0.2mag brighter for double profile BCGs. This result indicates that extra-light for double profile BCGs does not come from the inner region but from the outer regions of these galaxies. The best-fit slope of the Kormendy relation for the whole sample is a = 3.13 ± 0.04. However, when fitted separately, single and double profile BCGs show different slopes: a single = 3.29 ± 0.06 and a double = 2.79 ± 0.08. Also, the logarithmic slope of the metric luminosity α is higher in double profile BCGs (αdouble = 0.65 ± 0.12) than in single profile BCGs (αsingle = 0.59 ± 0.14). The mean isophote outer ellipticity (calculated at μ ∼ 24magarcsec -2) is higher in double profile BCGs (e double = 0.30 ± 0.10) than in single profile BCGs (e single = 0.26 ± 0.11). Similarly, the mean absolute value of inner minus outer ellipticity is also higher in double profile BCGs. From a subsample of 24 BCGs, we found strong evidence that extra-light at intermediate radii in double profile BCGs is related to the presence of a faint stellar envelope. Similarly, from another subsample of 12 BCGs we also found that extra-light is related to star formation. On the other hand, we did not find differences between these two BCG categories when we compared global cluster properties such as the BCG-projected position relative to the cluster X-ray center emission, X-ray luminosity, or BCG orientation with respect to the cluster position angle. © 2011. The American Astronomical Society. All rights reserved. Source


Cecere M.,Institute Investigaciones en Astronomia Teorica y Experimental IATE | Cecere M.,CONICET | Zurbriggen E.,Institute Investigaciones en Astronomia Teorica y Experimental IATE | Zurbriggen E.,CONICET | And 6 more authors.
Astrophysical Journal | Year: 2015

Supra-arcade downflows (SADs) are sunward, generally dark, plasma density depletions originated above posteruption flare arcades. In this paper, using 3D MHD simulations we investigate whether the SAD cavities can be produced by a direct combination of the tearing mode and Kelvin-Helmholtz instabilities leading to a turbulent current sheet (CS) medium or if the current sheet is merely the background where SADs are produced, triggered by an impulsive deposition of energy. We find that to give an account of the observational dark lane structures an addition of local energy, provided by a reconnection event, is required. We suggest that there may be a closed relation between characteristic SAD sizes and CS widths that must be satisfied to obtain an observable SAD. © 2015. The American Astronomical Society. All rights reserved. Source

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