We present a census of variable stars in six M31 dwarf spheroidal satellites observed with the Hubble Space Telescope. We detect 870 RR Lyrae (RRL) stars in the fields of And I (296), II (251), III (111), XV (117), XVI (8), and XXVIII (87). We also detect a total of 15 Anomalous Cepheids, three eclipsing binaries, and seven field RRL stars compatible with being members of the M31 halo or the Giant Stellar Stream. We derive robust and homogeneous distances to the six galaxies using different methods based on the properties of the RRL stars. Working with the up-to-date set of Period-Wesenheit (I, B-I) relations published by Marconi et al., we obtain distance moduli of {mu}0=[24.49, 24.16, 24.36, 24.42, 23.70, 24.43]mag (respectively), with systematic uncertainties of 0.08mag and statistical uncertainties <0.11mag. We have considered an enlarged sample of 16 M31 satellites with published variability studies, and compared their pulsational observables (e.g., periods and amplitudes) with those of 15 Milky Way satellites for which similar data are available. The properties of the (strictly old) RRL in both satellite systems do not show any significant difference. In particular, we found a strikingly similar correlation between the mean period distribution of the fundamental RRL pulsators (RRab) and the mean metallicities of the galaxies. This indicates that the old RRL progenitors were similar at the early stage in the two environments, suggesting very similar characteristics for the earliest stages of evolution of both satellite systems.
The relationship between interstellar extinction and distance in the direction of dark clouds in the areas around the open cluster IC 348 and the association Per OB2 is determined using the results of photoelectric photometry of 189 stars in the Vilnius photometric system.
We present the results of an ISOCAM survey of the Chamaeleon I dark cloud conducted in two broad-band filters at 6.7 and 14.3{mu}m. In an area of 0.59deg^2^. we have detected a total of 282 mid-IR sources with 103 sources observed in both filters. Combining the ISOCAM observations with the I, J, and K_s_ data obtained with DENIS, we have found 108 pre-main-sequence (PMS) stars in the region, of which 34 were previously unidentified. Several of these newly discovered young stellar objects are relatively faint suggesting a population in Cha I of very low mass objects that probably includes brown dwarfs in their early contraction phases. Finally, most of the PMS stars show the spectral index computed between 2.2 and 14.3{mu}m typical of Class II sources. The luminosity function (LF) derived for our detected PMS stars is discussed.
File table1 contains the list of the 212 ISOCAM sources recognized as members of the rho Ophiuchi embedded cluster. It lists their J2000 coordinates, flux densities at 6.7 and 14.3 micron and associated rms uncertainties, as well as the corresponding near-infrared identifications and the adopted IR classes (Class I, II or III).
We present results from an ISOCAM survey in the two broadband filters LW2 (5-8.5um) and LW3 (12-18um) of a 19'x16' field called Serp_NH3 centred on the optical group Serpens/G3-G6. A total of 186 sources were detected in the 6.7um band and/or the 14.3um band to a limiting sensitivity of ~2mJy. These have been cross-correlated with the 2MASS catalogue and are all listed in table1. Deep follow-up photometry in the Ks band obtained with Arnica at the Nordic Optical Telescope (NOT) is listed in table2. Deep L' band photometry of selected sources using SIRCA at the NOT is listed in table3. Continuum emission at 1.3mm and 3.6cm was observed with IRAM and VLA, respectively, and deep imaging in the 2.12um S(1) line of H2 was obtained with NOTCam at the NOT. We find strong evidence for a stellar population of 31 Class II sources (listed in table5), 5 flat-spectrum sources, 5 Class I sources (listed in table4), and two Class 0 sources. Our method does not sample the Class III sources.
We present results from an ISOCAM survey in the two broad band filters LW2 (5-8.5{mu}m) and LW3 (12-18{mu}m) of a 0.13 square degree coverage of the Serpens Main Cloud Core. A total of 392 sources were detected in the 6.7{mu}m band and 139 in the 14.3{mu}m band to a limiting sensitivity of ~2mJy. We identified 53 Young Stellar Objects (YSOs) with mid-IR excess from the single colour index [14.3/6.7], and 8 additional YSOs from the H-K/K-m_6.7_ diagram. Only 32 of these 61 sources were previously known to be YSO candidates.
We present a study of ISOGAL sources in the "intermediate" galactic bulge (|l|<2{deg}, |b|~1{deg}-4{deg}), observed by ISOCAM at 7 and 15{mu}m. In combination with near-infrared (I, J, Ks) data of DENIS survey, complemented by 2MASS data, we discuss the nature of the ISOGAL sources, their luminosities, the interstellar extinction and the mass-loss rates. A large fraction of the 1464 detected sources at 15{mu}m are AGB stars above the RGB tip, a number of them show an excess in ([7]-[15])_0_ and (Ks-[15])_0_ colours, characteristic of mass-loss. The latter, especially (Ks-[15])_0_, provide estimates of the mass-loss rates and show their distribution in the range 10^-8^ to 10^-5^M_{sun}_/yr.
Compact elliptical galaxies form a rare class of stellar system (~30 presently known) characterized by high stellar densities and small sizes and often harboring metal-rich stars. They were thought to form through tidal stripping of massive progenitors, until two isolated objects were discovered where massive galaxies performing the stripping could not be identified. By mining astronomical survey data, we have now found 195 compact elliptical galaxies in all types of environment. They all share similar dynamical and stellar population properties. Dynamical analysis for nonisolated galaxies demonstrates the feasibility of their ejection from host clusters and groups by three-body encounters, which is in agreement with numerical simulations. Hence, isolated compact elliptical and isolated quiescent dwarf galaxies are tidally stripped systems that ran away from their hosts.
This article presents the study of the light curves extracted from the MACHO database of a sample of stars observed by the Infrared Space Observatory in the Small Magellanic Cloud. These stars belong to the ISO Mini-Survey catalogue of the Magellanic Clouds (ISO MCMS, Loup et al., in preparation). Most of them are in the asymptotic giant branch (AGB) and supergiant phases. The dominant period and amplitude of pulsation have been derived and the stars have been classified as Mira or Semi Regular pulsators.
The Canada-France Redshift Survey 1452+52 field has been deeply imaged with the Infrared Space Observatory using ISOCAM through the LW3 filter (1218 {mu}m). Careful data analysis and comparison with deep optical and radio data have allowed us to generate a catalog of 78 15 {mu}m sources with both radio and optical identifications. They are redder and lie at higher redshift than I-band-selected galaxies, with most of them being star-forming galaxies. We have considered the galaxies detected at radio and 15 {mu}m wavelengths, which potentially include all strong and heavily extincted starbursts, up to z=1. Spectral energy distributions (SEDs) for each of the sources have been derived using deep radio, mid-IR, near-IR, optical, and UV photometry. The sources were then spectrally classified by comparing with SEDs of well-known nearby galaxies. By deriving their far-IR luminosities by interpolation, we can estimate their star formation rate (SFR) in a way that does not depend sensitively on the extinction.
