J. Borissova

Bimodality and Gaps on Globular Cluster Horizontal Branches. II. The Cases of NGC 6229, NGC 1851, and NGC 2808

The outer halo globular cluster NGC 6229 has a peculiar horizontal-branch (HB) morphology, with clear indications of a bimodal HB and a gap on the blue HB. In this paper, we present extensive synthetic HB simulations to determine whether peculiar distributions in the underlying physical parameters are needed to explain the observed HB morphology. We find that a unimodal mass distribution along the HB can satisfactorily account for the observed HB bimodality, provided the mass dispersion is substantially larger than usually inferred for the Galactic globular clusters. In this case, NGC 6229 should have a well-populated, extended blue tail. A truly bimodal distribution in HB masses can also satisfactorily account for the observed HB morphology, although in this case the existence of an extended blue tail is not necessarily implied. The other two well-known bimodal-HB clusters, NGC 1851 and NGC 2808, are briefly analyzed. While the HB morphology of NGC 1851 can also be reproduced with a unimodal mass distribution assuming a large mass dispersion, the same is not true of NGC 2808, for which a bimodal, and possibly multimodal, mass distribution seems definitely required. The problem of gaps on the blue HB is also discussed. Applying the standard Hawarden and Newell χ2 test, we find that the NGC 6229 gap is significant at the 99.7% level. However, in a set of 1000 simulations, blue-HB gaps comparable to the observed one are present in ~6%-9% of all cases. We employ a new and simple formalism, based on the binomial distribution, to explain the origin of this discrepancy, and conclude that Hawardens method, in general, substantially overestimates the statistical significance of gaps.

IC 10: More evidence that it is a blue compact dwarf

We present optical spectroscopy of Hii regions in the Local Group galaxy IC 10 and UBVR photometry of foreground stars in three fields towards this galaxy. From these data, we find that the foreground reddening due to the Milky Way is

Groups of Galaxies in the Nearby Universe

E(B-V)=0.77\pm 0.07 \mathrm{mag}

Kinematics of the ionized gas in the Local Group irregular galaxy IC 1613

. We find that IC 10 contains considerable internal dust, which qualitatively explains the variety of reddening values found by studies of its different stellar populations. Based upon our foreground reddening, IC 10 has intrinsic photometric properties like those of a blue compact dwarf galaxy, and not those of a dwarf irregular. This result is consistent with much evidence that IC 10 is in the throes of a starburst that began at least

The outer-halo globular cluster NGC 6229 – IV. Variable stars

10 \mathrm{Myr}

The first known Mira-type variable star in IC 1613

ago. We also report the discovery of a new WR star in the Hii region HL111c.

Extending the Red Giant Branch versus Metallicity Calibration toward Metal-poor Systems: Near-Infrared Photometry of the Galactic Globular Clusters M56 and M15*

For every galaxy in the field or in clusters, there are about three galaxies in groups. Therefore, the evolution of most galaxies actually happens in groups. The Milky Way resides in a group, and groups can be found at high redshift. The current generation of 10-m-class telescopes and space facilities allows us to study members of nearby groups with exquisite detail, and their properties can be correlated with the global properties of their host group. Finally, groups are relevant for cosmology, since they trace largescale structures better than clusters, and the evolution of groups and clusters may be related.

Stellar Photometry of the Globular Cluster NGC 6229.I.Data Reduction and Morphology of the Brighter Part of the CMD

We present H α and [Sii] observations for the Local Group irregular galaxy IC 1613 using the PUMA scanning Fabry-Perot interferometer. Our goal is to analyze the kinematics of the ionized gas in the complex sample of superbubbles located in the whole extension of our field (10´), which includes most of the optical emission of this galaxy, and to study the inter-relationship between young stellar associations and nebulae based on a previous study that we have made on the stellar associations of the central region of this galaxy. The ionized gas in this galaxy is distributed in classical Hii regions and in a series of superbubbles (also called giant shells) covering a large fraction of the optical extent of the galaxy. We present a catalog of kinematical properties of both the Hii regions of this galaxy and the superbubbles. We have also compared the kinematics of the ionized gas in Hii regions to search for possible dynamic differences between neutral and ionized gas.

The Local Group dwarf irregular galaxy IC 1613 - I. The young stellar content

We present time-series B, V photometry of NGC 6229, obtained with the purpose of providing the first extensive CCD variability study of this cluster. As a result, we were able to obtain periods for all NGC 6229 variables, with the exception of five stars from the Borissova et al. (1997) candidate list located very close to the cluster center. Two variable stars suspected by Carney, Fullton, & Trammell (1991) are first-overtone RR Lyrae (RRc) stars, whereas seven of the 12 candidates from Borissova et al. (1997) are confirmed variables—three of them being fundamental RR Lyrae (RRab) pulsators, two first-overtone pulsators, one eclipsing binary (most likely an Algol system) and one bright star whose variability status could not be satisfactorily determined. A new image subtraction method (ISM) suggested by Alard (1999) has been employed which, together with the Welch & Stetson (1993) technique, has allowed us to discover twelve new RR Lyrae variables in the cluster, for which ephemerides are provided. Ten of these are RRab’s, whereas the other two are RRc’s. As originally suggested by Mayer (1961), NGC 6229 is clearly an Oosterhoff type I globular cluster. We also confirm that V8 is a Population II Cepheid of the W Virginis type, and suspect that this is the case for V22 as well. The physical properties of the NGC 6229 RR Lyrae population are compared against those of M3 (NGC 5272) using several different methods, including a standard period-shift analysis. Possible differences between these two clusters are discussed.

The influence of massive stars in the interstellar medium of IC 1613: the supernova remnant S8 and the nebula S3 associated with a WO star.

King et al. (1999) discovered Nova 1999 in IC 1613 at the Lick Observatory. Both Fugazza et al. ([CITE]) and Borissova et al. ([CITE]) questioned this classification, because they were able to detect the star on images obtained in previous years. In infrared frames taken on Oct. 15, 1998, Nova 1999 has