We report the discovery of a mid-infrared outburst in a young stellar object (YSO) with an amplitude close to 8 mag at λ ≈ 4.6 μm. WISEA J142238.82−611553.7 is one of 23 highly variable Wide-field Infrared Survey Explorer (WISE) sources... more
We report the discovery of a mid-infrared outburst in a young stellar object (YSO) with an amplitude close to 8 mag at λ ≈ 4.6 μm. WISEA J142238.82−611553.7 is one of 23 highly variable Wide-field Infrared Survey Explorer (WISE) sources discovered in a search of infrared dark clouds (IRDCs). It lies within the small IRDC G313.671−0.309 (d ≈2.6 kpc), seen by the Herschel/Hi-Gal survey as a compact massive cloud core that may have been measurably warmed by the event. Pre-outburst data from Spitzer in 2004 suggest it is a class I YSO, a view supported by observation of weak 2.12 μm H2 emission in an otherwise featureless red continuum spectrum in 2019 (6 mag below the peak in Ks). Spitzer, WISE, and VISTA Variables in the Via Lactea (VVV) data show that the outburst began by 2006 and has a duration >13 yr, with a fairly flat peak from 2010 to 2014. The low pre-outburst luminosity implies a low-mass progenitor. The outburst luminosity of a few × 102 L⊙ is consistent with an accretion...
We report a search and analysis of obscured cluster candidates in the ‘VISTA Variables in the Via Lactea eXtended (VVVX)’ ESO Public Survey area encompassing the region between 229${_{.}^{\circ}}$4 < l < 295${_{.}^{\circ}}$2 and... more
We report a search and analysis of obscured cluster candidates in the ‘VISTA Variables in the Via Lactea eXtended (VVVX)’ ESO Public Survey area encompassing the region between 229${_{.}^{\circ}}$4 < l < 295${_{.}^{\circ}}$2 and −4${_{.}^{\circ}}$3 < b < 4${_{.}^{\circ}}$4 of the southern Galactic disc. We discover and propose 88 new clusters. We improve the completeness of the embedded cluster population in this region, adding small size (linear diameters of 0.2–1.4 pc) and relatively far objects (heliocentric distance between 2 and 4 kpc) to existing catalogues. Nine candidates are proposed to be older open cluster candidates. Three of them (VVVX CL 204, CL 207, CL 208) have sufficient numbers of well-resolved stellar members to allow us to determine some basic cluster parameters. We confirm their nature as older, low-mass open clusters. Photometric analysis of 15 known clusters shows that they have ages above 20 Myr, and masses below 2000 M⊙: in general, their prope...
Moderately deep ground based UBV images are used to investigate the OB associations and star clusters in IC 1613. Fifty eight OB associations with sizes between 30 and 130 pc are outlined. The iteration between associations and... more
Moderately deep ground based UBV images are used to investigate the OB associations and star clusters in IC 1613. Fifty eight OB associations with sizes between 30 and 130 pc are outlined. The iteration between associations and superbubbles in IC 1613 was analyzed. The lack of star clusters was confirmed.
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We present a preliminary report on the first deep near infrared photometry of 2MASS GC 01 and 2MASS GC 02 - new Galactic globular cluster candidates, discovered by the 2MASS. The red giant branch slopes yielded [Fe/H]=-0.42 ± 0.15 dex and... more
We present a preliminary report on the first deep near infrared photometry of 2MASS GC 01 and 2MASS GC 02 - new Galactic globular cluster candidates, discovered by the 2MASS. The red giant branch slopes yielded [Fe/H]=-0.42 ± 0.15 dex and [Fe/H]=-0.66 ± 0.17 dex, respectively for GC 01 and GC 02. We estimated the reddening towards GC 01 and GC 02: E(B - V) = 5.36 ± 0.20, and E(B - V) = 4.55 ± 0.17. The calculated distance moduli to the clusters are: (m - M)0 = 13.53 ± 0.27 and (m - M)0 = 14.53 ± 0.31 for GC 01 and GC 02. Our best fit for the radial surface brightness profile of GC 02 yields: lg(rc) = 1.40, lg(rh) = 1.54, lg(rt) = 1.31, and c=1.60. CC 01 is less concentrated: lg(rc) = 1.63, lg(rh) = 1.7, lg(rt) = 1.25, and c=1.41.
We have searched for supernova remnants (SNRs) in the irregular galaxies IC 10 and NGC 4449 by means of Fabry-Perot interferometry in Hα and [SII] lines, complemented by radio continuum observations. We find several new SNR candidates in... more
We have searched for supernova remnants (SNRs) in the irregular galaxies IC 10 and NGC 4449 by means of Fabry-Perot interferometry in Hα and [SII] lines, complemented by radio continuum observations. We find several new SNR candidates in each galaxy in addition to the known ones. Although these galaxies have several common properties, the distributions of SNRs in each galaxy is different. This shows that the star formation mechanisms in these galaxies act in different ways, in favor of the formation of a large nebular HII complex in IC 10, similar to 30 Dor in the Large Magellanic Cloud. We are studying the conditions over which these different star formation histories take place.
ABSTRACT We have presented the preliminary results of the first spectroscopic observations of the galactic globular clusters 2MASS GC01 and 2MASS GC02. The metallicity, radial velocities and distances to the clusters are determined.
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A simple and robust method, based on stellar surface density was proposed in order to search for undetected star clusters in our Galaxy on the base of the 2MASS catalogue. The zone of the sky of galactic latitude between -80 and -40... more
A simple and robust method, based on stellar surface density was proposed in order to search for undetected star clusters in our Galaxy on the base of the 2MASS catalogue. The zone of the sky of galactic latitude between -80 and -40 degree was choosen to test the method. As a result we identify approx. 30% of suspected cluster candidtes.
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Research Interests:
We present a study of abundances of two hidden Galactic globular clus- ters: Mercer 5 and 2MASS GC02, using high-resolution (IR) spectra. We measure accurate radial velocities of vr = +194 ± 0.3 km s-1 for Mer- cer 5 star 1 and vr = +177... more
We present a study of abundances of two hidden Galactic globular clus- ters: Mercer 5 and 2MASS GC02, using high-resolution (IR) spectra. We measure accurate radial velocities of vr = +194 ± 0.3 km s-1 for Mer- cer 5 star 1 and vr = +177 ± 0.3 km s-1 for Mercer 5 star 2. We find [Fe/H] = -1.00 ± 0.02 dex and average a - elements enhancement of +0.40 ± 0.02 dex for Mercer 5, while for 2MASS GC02 we only make a qualitative analysis, due to insufficient signal to noise of the target spectra.
Here we present survey of proper motion stars towards the Galactic Bulge and an adjacent plane region base on VISTA-VVV data. The searching method based on cross-matching photometric Ks-band CASU catalogs. The most interesting discoveries... more
Here we present survey of proper motion stars towards the Galactic Bulge and an adjacent plane region base on VISTA-VVV data. The searching method based on cross-matching photometric Ks-band CASU catalogs. The most interesting discoveries are shown.
The spectroscopic observations were taken with the FORS1 multi-slit spectrograph at the ESO Very Large Telescopte (VLT) Unit Telescope 1 (UT1), during the nights of 10 and 11 January 2003. (2 data files).
In Paper I (Cat. J/A+A/423/97) we presented radial velocities, metallicities and K-band magnitudes of 74 RR Lyrae stars in the inner regions of the LMC. The optical low resolution spectra were obtained with the FORS1 at the ESO VLT and... more
In Paper I (Cat. J/A+A/423/97) we presented radial velocities, metallicities and K-band magnitudes of 74 RR Lyrae stars in the inner regions of the LMC. The optical low resolution spectra were obtained with the FORS1 at the ESO VLT and near-IR photometry images with the SOFI infrared array at the ESO NTT. We have chosen to extend this sample by using the MACHO (Alcock et al., 2000, Cat. J/ApJ/542/257) and OGLE (Zebrun et al., 2001AcA....51..317Z) databases to seven fields of the LMC bar, at distances from 0.4 to 2.5 degrees away from the rotation center (Soszynski et al., 2003, Cat. J/AcA/53/93). Two of these new fields are centered on the LMC clusters NGC 1835 and NGC 2019. We also observed additional stars in the fields LMC-4, LMC-9 and LMC-14 defined in Paper I. (1 data file).
This paper presents new (single-epoch) J-band and (multi-epoch) Ks-band photometry of RR Lyr stars in 7 different LMC fields, observed with the near-IR camera SOFI at ESO's New Technology Telescope. Additional Ks-band data for another... more
This paper presents new (single-epoch) J-band and (multi-epoch) Ks-band photometry of RR Lyr stars in 7 different LMC fields, observed with the near-IR camera SOFI at ESO's New Technology Telescope. Additional Ks-band data for another two LMC fields were taken with the ISPI infrared array at CTIO's Blanco 4m telescope. The near-IR photometry was cross-correlated with the MACHO and OGLE databases, resulting in a catalog of 62 RR Lyr stars with BV RIJKs photometry. A subsample of 50 stars also has spectroscopically mea sured metallicities. In the deep JK color-magnitude diagrams of 7 fields, red giant branch, red clump and RR Lyr stars are detected. (2 data files).
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ABSTRACT We present observations of the extended optical counterpart of the bright, elongated ULX in the interacting galaxy pair NGC 5953/54 using the FLAMES-ARGUS integral field spectrograph on the VLT. We describe spectroscopic and... more
ABSTRACT We present observations of the extended optical counterpart of the bright, elongated ULX in the interacting galaxy pair NGC 5953/54 using the FLAMES-ARGUS integral field spectrograph on the VLT. We describe spectroscopic and spatial information of the ionized surroundings of this ULX in order to distinguish between two possible scenarios: a stellar-mass black hole binary or an intermediate-mass (~ 50 solar masses) black hole.
We are reporting some recent results from our long-term program aimed at characterizing the obscured present-day star cluster population in the Galaxy. Our goal is to expand the current census of the Milky Way's inner stellar disk to... more
We are reporting some recent results from our long-term program aimed at characterizing the obscured present-day star cluster population in the Galaxy. Our goal is to expand the current census of the Milky Way's inner stellar disk to guide models seeking to understand the structure and recent star-formation history of our Galaxy. The immediate goal is to derive accurate cluster physical parameters using precise infrared photometry and spectroscopy. So far, we observed approximately 60 star cluster candidates selected from different infrared catalogs. Their nature, reddening, distance, age and mass are analyzed. Two of them, Mercer 3 and Mercer 5, are new obscured Milky Way globular clusters. Among the newly identified open clusters, the objects [DBS2003] 179, Mercer 23, Mercer 30, Mercer 70, and [DBS2003] 106 are particularly interesting because they contain massive young OB and Wolf–Rayet stars with strong emission lines.
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ABSTRACT The most accurate method of age determination for resolved or partially resolved stellar clusters is based on color-magnitude diagrams (CMD). However, when the main sequence turnoff is not available or clearly identifiable, the... more
ABSTRACT The most accurate method of age determination for resolved or partially resolved stellar clusters is based on color-magnitude diagrams (CMD). However, when the main sequence turnoff is not available or clearly identifiable, the age determined by isochrone fitting is affected by large errors. We used the MASSCLEAN package to perform 4 million Monte Carlo simulations in order to generate realistic looking CMDs. They mimic the observational photometric errors, and show the density of stars in the CMD plane. We use these CMD templates to analyze the newly discovered stellar clusters/cluster candidates from the Vista Variables in the Via Lactea (VVV) Survey. Since the majority of the new VVV clusters are low mass, the upper end of the stellar mass distribution is affected by stochastic fluctuations, which generates a large gap in the infrared CMD. We explore this gap in the J and K_s bands by performing 1 million Monte Carlo simulations. Combining the traditional isochrone fitting, CMD templates, and the magnitude distribution with respect to the infrared gap we were able to put better constrains on age, distance, and extinction for 7 VVV clusters. This material is based upon work supported by the National Science Foundation under Grant No. 0607497 and 1009550.
ABSTRACT Is there a maximum universal stellar mass, or might the maximum stellar mass in a cluster be tied to the mass of the associated cluster? Direct measurements of the maximum stellar mass of hundreds of young stellar clusters would... more
ABSTRACT Is there a maximum universal stellar mass, or might the maximum stellar mass in a cluster be tied to the mass of the associated cluster? Direct measurements of the maximum stellar mass of hundreds of young stellar clusters would help us to answer this fundamental question. However, such information does not presently exist. We are mindful that the most massive star in a stellar cluster can have a strong influence on the integrated magnitudes and colors of their host stellar cluster, especially clusters in the low-mass range. Thinking strategically, this color variation provides us with a mechanism for divulging the properties of that most massive star. We performed 25 million MASSCLEAN Monte Carlo simulations of stellar clusters in the 200-1000 M_Sun range in the U, B, and V bands. These simulations were then used to estimate the mass of the most massive star for 40 young, low-mass LMC clusters. In a similar way, the integrated colors and magnitudes in VISTA&#39;s Z, Y, J, H, and Ks bands can also be used to estimate the mass of the most massive star in VISTA-identified stellar clusters. Is the IMF for one hundred young 1000 solar mass clusters the same at the high end as ten young 10,000 solar mass clusters? Using the VISTA&#39;s clusters, we intend to answer the question, &quot;Does the lower mass of a stellar cluster artificially steepen the high-mass IMF?&quot;.
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... BRANCH VERSUS METALLICITY CALIBRATION TOWARD METAL-POOR SYSTEMS: NEAR-INFRARED PHOTOMETRY OF THE GALACTIC GLOBULAR CLUSTERS M56 AND M151VALENTIN D. IVANOV ... The basic data for the clusters are listed in Table 1 (Harris 19962). ...
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Many attempts have been made to carry out a complete observational census of Milky Way star clusters based on recent near- and mid-infrared surveys. However, more clusters are still being discovered, indicating that existing catalogs are... more
Many attempts have been made to carry out a complete observational census of Milky Way star clusters based on recent near- and mid-infrared surveys. However, more clusters are still being discovered, indicating that existing catalogs are incomplete. We attempt to estimate the total number of supermassive (SM; Mcl ≥ 104 M⊙) clusters in the Galaxy, and to improve the yield from the automated cluster searches. Assuming that the ‘local’ census of SM clusters is complete, and that their surface density accross the disk follows that of the stars, we predict that the Milky Way contains ≥81 ± 21 SM clusters. We apply a cluster-detection algorithm to the 2mass Point Source Catalog after a preliminary color and/or magnitude selection of the point sources to improves the surface-density cluster-to-field contrast. Our algorithm identified 94 new candidates, and re-identified 34 known clusters. During the visual inspection, we detected an additional 41 new candidates, and re-identified 32 known ...
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One of the main goals of the “VVV–Vista Variables in the Via Lactea” ESO Large Survey is to search for new star clusters of different ages. In order to trace the early stages of star clusters formation we carrying out a survey of infrared... more
One of the main goals of the “VVV–Vista Variables in the Via Lactea” ESO Large Survey is to search for new star clusters of different ages. In order to trace the early stages of star clusters formation we carrying out a survey of infrared star cluster candidates and stellar groups in ...
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The variable stars in the Large Magellanic Cloud star cluster NGC 2257 are reinvestigated using photometry (to ~20th mag) of over 400 new B, V CCD images taken with the CTIO 0.9 m telescope on 14 nights in 2007 December and 2008 January.... more
The variable stars in the Large Magellanic Cloud star cluster NGC 2257 are reinvestigated using photometry (to ~20th mag) of over 400 new B, V CCD images taken with the CTIO 0.9 m telescope on 14 nights in 2007 December and 2008 January. New period searches have been made using two independent algorithms (CLEAN, Period04); the resultant periods of most
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Research Interests:
Deep BV photometry for a large field covering the outer-halo globular cluster NGC 6229 is presented. For the first time, a colour-magnitude diagram (CMD) reaching below the main sequence turnoff has been obtained for this cluster.... more
Deep BV photometry for a large field covering the outer-halo globular cluster NGC 6229 is presented. For the first time, a colour-magnitude diagram (CMD) reaching below the main sequence turnoff has been obtained for this cluster. Previous results regarding the overall morphology of the horizontal and giant branches are confirmed. In addition, nine possible extreme horizontal-branch stars have been identified in our deep images, as well as thirty-three candidate blue stragglers. We also find the latter to be more centrally concentrated than subgiant branch stars covering the same range in V magnitude. A comparison of the cluster CMD with the M5 (NGC 5904) ridgeline from Sandquist et al. (1996) reveals that: i) NGC 6229 and M5 have essentially identical metallicities; ii) NGC 6229 and M5 have the same ages within the errors in spite of their different horizontal-branch morphologies.
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Research Interests:
... REFERENCES Aparicio, A., Gallart, C. 1995, AJ, 110, 2105 Aparicio, A. 1999, Proceeding of ... 1996, ApJ, 461, 713 Sandage, A. 1971, ApJ, 166, 13 Santangelo, M.,M. 1999, IAUC ... Ave, Tucson, AZ 85721 (vdivanov@as.arizona.edu)... more
... REFERENCES Aparicio, A., Gallart, C. 1995, AJ, 110, 2105 Aparicio, A. 1999, Proceeding of ... 1996, ApJ, 461, 713 Sandage, A. 1971, ApJ, 166, 13 Santangelo, M.,M. 1999, IAUC ... Ave, Tucson, AZ 85721 (vdivanov@as.arizona.edu) Margarita Valdez-Gutiérrez: Instituto Nacional ...
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... M. Catelan,1 HA Smith,2 BJ Pritzl,3 J. Borissova,4 C. Cacciari,5 R. Contreras,1 T. M. Corwin,6 N. De Lee,2 ME Escobar,1 AC Layden,7 C. Navarro,1 G. Prieto,1 R. Salinas,1,8 PB Stetson,9 AV ... According to the com-pilation of variable... more
... M. Catelan,1 HA Smith,2 BJ Pritzl,3 J. Borissova,4 C. Cacciari,5 R. Contreras,1 T. M. Corwin,6 N. De Lee,2 ME Escobar,1 AC Layden,7 C. Navarro,1 G. Prieto,1 R. Salinas,1,8 PB Stetson,9 AV ... According to the com-pilation of variable stars in globular clusters by Clement et al. ...