arXiv subjects

Valentin D. Ivanov

Publications and source records attributed to Valentin D. Ivanov.

103 records · Page 6Linked to original sources

arXiv2005

Common Proper Motion Search for Faint Companions Around Early-Type Field Stars - Progress Report

The multiplicity of early-type stars is still not well established. The derived binary fraction is different for individual star forming regions, suggesting a connection with the age and the environment conditions. The few studies that have investigated this connection do not provide conclusive results. To fill in this gap, we started the first detailed adaptive-optic-assisted imaging survey of early-type field stars to derive their multiplicity in a homogeneous way. The sample has been extracted from the Hipparcos Catalog and consists of 341 BA-type stars within ~300 pc from the Sun. We report the current status of the survey and describe a Monte-Carlo simulation that estimates the completeness of our companion detection.

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arXiv2005

Red giant branch stars as probes of stellar populations. II. Properties of the newly discovered globular cluster GLIMPSE-C01

Deep near infrared photometry of the newly discovered Galactic globular Cluster GLIMPSE-C01 is reported. We derived for the first time the metal abundance of this object from the slope of the RGB: [Fe/H]=-1.61+/-0.14 in the scale of Zinn (as implemented in Harris 1996), [Fe/H]=-1.44+/-0.12 in the scale of Caretta & Gratton (1997), and [Fe/H]=-1.12+/-0.12 in the scale of Ferraro et al. (1999). The tip and the clump of the red giant branch were used to confirm the estimates of Kobulnicky et al. (2005), placing the cluster at D~3.7+/-0.8 kpc, behind A_v~15 mag of visual extinction. The best fit to the radial surface brightness profile with a single-mass King's model (1962) yielded core radius r_c=0.78 arcmin, tidal radius r_t=27 arcmin, and central concentration c=1.54. Finally, we estimate the number of the "missing" globulars in the central region of the Milky Way. Based on the spatial distribution of the known clusters, and assuming radial symmetry around the Galactic center, we conclude that the Milky Way contains at least 10+/-3 undiscovered objects. The distribution of known clusters in the bulge seem to resemble the orientation of the Milky Way bar.

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arXiv2003

A Medium-Resolution Near-Infrared Spectral Library of Late Type Stars: I

We present an empirical infrared spectral library of medium resolution (R~2000-3000) H (1.6 micron) and K (2.2 micron) band spectra of 218 red stars, spanning a range of [Fe/H] from ~-2.2 to ~+0.3. The sample includes Galactic disk stars, bulge stars from Baade's window, and red giants from Galactic globular clusters. We report the values of 19 indices covering 12 spectral features measured from the spectra in the library. Finally, we derive calibrations to estimate the effective temperature, and diagnostic relationships to determine the luminosity classes of individual stars from near-infrared spectra. This paper is part of a larger effort aimed at building a near-IR spectral library to be incorporated in population synthesis models, as well as, at testing synthetic stellar spectra.

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arXiv2003

Spectral Energy Distributions of Seyfert Nuclei

We present nuclear spectral energy distributions (SEDs) in the range 0.4-16micron for an expanded CfA sample of Seyfert galaxies. The spectral indices from 1-16micron range from alpha_IR 0.9 to 3.8. The shapes of the spectra are correlated with Seyfert type in the sense that steeper nuclear SEDs (nu*f_nu increasing with increasing wavelength) tend to be found in Seyfert 2s and flatter SEDs (nu *f_nu constant) in Seyfert 1-1.5s. The galaxies optically classified as Seyferts 1.8s and 1.9s display values of alpha_IR as in type 1 objects, or values intermediate between those of Seyfert 1s and Seyfert 2s. The intermediate SEDs of many Seyfert 1.8-1.9s may be consistent with the presence of a pure Seyfert 1 viewed through a moderate amount (A_V <5mag) of foreground galaxy extinction. We find, however, that between 10 and 20% of galaxies with broad optical line components have steep infrared SEDs. Torus models usually adopt high equatorial opacities to reproduce the infrared properties of Seyfert 1s and 2s, resulting in a dichotomy of infrared SEDs (flat for type 1s, and steep for type 2s). Such a dichotomy, however, is not observed in our sample. The wide range of spectral indices observed in the type 2 objects, the lack of extremely steep SEDs, and the large numbers of objects with intermediate spectral indices cannot be reconciled with predictions from existing optically thick torus models. We discuss possible modifications to improve torus models, including low optical depth tori, clumpy dusty tori, and high-optical-depth tori with an extended optically thin component.

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arXiv2002

T Tauri Stars in the Small Magellanic Cloud

The Small Magellanic Cloud (SMC) is an excellent laboratory to study the formation of solar-mass stars in a low-metallicity environment, similar to the conditions expected in the early phases of galactic evolution. Here we present preliminary results from a search for low-mass pre-main-sequence stars in the SMC based on Hubble Space Telescope archival data. Candidates are selected on the basis of their H_alpha emission and location in the [(F675W-F814W), F814W] color-magnitude diagram. We discuss characteristics of our candidate T Tauri sample and possible follow up work.

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arXiv2002

Deep I-band Imaging of z=5.99 Quasar

Deep I-band imaging was carried out to search for the optical counterpart of the X-ray jet candidate near SDSS 1306+0356, reported by Schwartz (2002, astro-ph/0202190). The data suggest that the extended X-ray source may be a jet, related to a galaxy rather than to the quasar itself.

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arXiv2002

Red Giant Branch Stars as Probes of Stellar Populations I: 2MASS Calibration and Application to 2MASS GC01

The near-infrared behavior of the red giant branch (RGB hereafter) as a function of abundance is examined with an unprecedented large sample of 27 Galactic globular clusters with Two Micron All Sky Survey photometry. We propose a new simplified analyses, involving the zero point of the RGB slope fit, and derive calibrations for the RGB slope, zero point, and tip. The weak metallicity sensitivity of the zero point leads to a ``fan''-like diagram for obtaining the abundance distributions in resolved stellar systems, and reddening estimates. Finally, we apply the new calibrations to the recently discovered Galactic globular cluster 2MASS GC01, to derive [Fe/H]_H96=-1.19+/-0.38 mag. The uncertainty is dominated by the severe foreground contamination. We estimate an extinction of A_V=21.07+/-2.20 mag toward the cluster.

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arXiv2002

Optical and Infrared Spectroscopy of SN 1999ee and SN 1999ex

We report optical and infrared spectroscopic observations of the Type Ia SN 1999ee and the Type Ib/c SN 1999ex, both of which were hosted by the galaxy IC 5179. For SN 1999ee we obtained a continuous sequence with an unprecedented wavelength and temporal coverage beginning 9 days before maximum light and extending through day 42. Before maximum light SN 1999ee displayed a normal spectrum with a strong Si II 6355 absorption, thus showing that not all slow-declining SNe are spectroscopically peculiar at these evolutionary phases. A comparative study of the infrared spectra of SN 1999ee and other Type Ia supernovae shows that there is a remarkable homogeneity among the Branch-normal SNe Ia during their first 60 days of evolution. SN 1991bg-like objects, on the other hand, display spectroscopic peculiarities at infrared wavelengths. SN 1999ex was characterized by the lack of hydrogen lines, weak optical He I lines, and strong He I 10830,20581, thus providing an example of an intermediate case between pure Ib and Ic supernovae. We conclude therefore that SN 1999ex provides first clear evidence for a link between the Ib and Ic classes and that there is a continuous spectroscopic sequence ranging from the He deficient SNe Ic to the SNe Ib which are characterized by strong optical He I lines.

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arXiv2000

Deep Near Infrared Photometry of New Galactic Globular Clusters

We present a preliminary report on the first deep infrared photometry of 2MASS GC01 and 2MASS GC02 (GC01 and GC02 hereafter) - new Galactic globular cluster (GC) candidates, discovered by the 2MASS. They both appear to be genuine disk GCs though highly obscured. The location of the two GCs suggests that they are metal rich - [Fe/H]~-0.5. We estimated their distance and reddening using the K_s-band brightness of the red giant branch (RGB) bump, and J-K_s color of the RGB at M_K=-3 mag: D=3.1+/-0.5, 3.9+/-0.6 kpc, and A_V=20.9+/-0.7, 17.2+/-1.2 mag, for GC01 and GC02 respectively. Variation in the metal abundance can change our results within 30-35%.

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arXiv2000

Testing the AGN-Starburst Connection in Seyfert Galaxies

We use the CO band at 2.3 micron to constrain the populations of young stars in the central regions of Seyfert galaxies. We report new CO band spectroscopy of 46 Seyfert galaxies. In most cases, the observed CO indices appear diluted by the presence of a non-stellar component (most likely, warm dust surrounding the active nucleus). We used JHKL aperture photometry to estimate the non-stellar contribution at 2.3 micron. We successfully corrected the CO band for the dilution for 16 galaxies which were not dominated by the non-stellar component. Comparing with CO indices measured in elliptical and purely starbursting galaxies, we find no evidence for strong starbursts in the majority of these galaxies.

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arXiv2000

On the Relation Between Peak Luminosity and Parent Population of Type Ia Supernovae: A New Tool for Probing the Ages of Distant Galaxies

We study the properties of Type Ia Supernovae (SNe Ia) as functions of the radial distance from their host galaxy centers. Using a sample of 62 SNe Ia with reliable luminosity, reddening, and decline rate determinations, we find no significant radial gradients of SNe Ia peak absolute magnitudes or decline rates in elliptical+S0 galaxies, suggesting that the diversity of SN properties is not related to the metallicity of their progenitors. We do find that the range in brightness and light curve width of supernovae in spiral galaxies extends to brighter, broader values. These results are interpreted as support for an age, but not metallicity, related origin of the diversity in SNe Ia. If confirmed with a larger and more accurate sample of data, the age-luminosity relation would offer a new and powerful tool to probe the ages and age gradients of stellar populations in galaxies at redshift as high as $z\sim1-2$. The absence of significant radial gradients in the peak $\rm (B-V)_0$ and $\rm (V-I)_0$ colors of SNe Ia supports the redding correction method of Phillips et al (1999). We find no radial gradient in residuals from the SN Ia luminosity-width relation, suggesting that the relation is not affected by properties of the progenitor populations and supporting the reliability of cosmological results based upon the use of SNe Ia as distance indicators.

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arXiv2000

Near Infrared Photometry of Galactic Globular Clusters M56 and M15. Extending the Red Giant Branch vs. Metallicity Calibration Towards Metal Poor Systems

Infrared JKs-band photometry of the Galactic globular clusters M15 and, for the first time, M56 is presented. We estimated the reddening (E(B-V)=0.18+/-0.08 mag) and distance modulus ((m-M)_V=15.43+/-0.30 mag) towards the poorly studied globular cluster M56. We combined our data with observations of other clusters from the literature (12 in total) to extend the [Fe/H] vs. Red Giant Branch (RGB) slope relation towards metal-poor clusters. Our best fit yields to [Fe/H]=-3.40(+/-0.22)-27.74(+/-2.35)x(RGB Slope), with an r.m.s.=0.20. The broader metallicity baseline greatly reduced the uncertainties compared to other existing calibrations. We confirmed a previously obtained calibration of the relation between the RGB color (J-Ks)_0(RGB) at M_Ks=-5.5 vs. [Fe/H]: [Fe/H]=-6.90(+/-0.99)+6.63(+/-1.05)x(J-Ks)_0(RGB) with an r.m.s.=0.33. Finally, using the new RGB slope calibration we estimated the abundance of the super metal-rich cluster Liller 1 [Fe/H]=+0.34+/-0.22.

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arXiv1999

An Infrared Determination of the Reddening and Distance to Dwingeloo 1

We present for the first time infrared observations of the nearby highly obscured galaxy Dwingeloo 1 (Dw1), including deep H-band imaging covering a total of 4.9x4.9 arcmin, together with J and Ks imaging of the central 2.5x2.5 arcmin. We used the small dispersion of the intrinsic infrared colors of spiral galaxies to determine an infrared H-band extinction of A_H = 0.47+/-0.11 mag towards Dw1. In using infrared colors, the uncertainties in the reddening and distance are reduced by a factor of three. The H-band magnitude corrected for extinction and the infrared Tully-Fisher relation are then used to estimate a distance modulus of (m-M)_0 = 28.62+/-0.27, and thus a distance of d = 5.3 {+0.7/-0.6} Mpc, which puts Dw1 at the far end of the IC342/Maffei 1 & 2 group. Our result is largely independent of the nature of the reddening law because we estimated both the reddening and the distance at the same wavelength range.

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