Variability is a common characteristic of pre-main-sequence stars (PMS). Near-IR variability surveys of young stellar objects (YSOs) can probe stellar and circumstellar environments and provide information about the dynamics of the on going magnetic and accretion processes. Furthermore, variability can be used as a tool to uncover new cluster members in star formation regions. We hope to achieve the deepest near-IR variability study of YSOs targeting the Rho Ophiuchi cluster. Fourteen epochs of observations were obtained with the Wide Field Camera (WFCAM) at the UKIRT telescope scheduled in a manner that allowed the study of variability on timescales of days, months, and years. Statistical tools, such as the multi-band cross correlation index and the reduced chi-square, were used to disentangle signals of variability from noise. Variability characteristics are compared to existing models of YSOs in order to relate them to physical processes, and then used to select new candidate members of this star-forming region. Variability in the near-IR is found to be present in 41% of the known population of Rho Ophiuchi recovered in our sample. The behaviours shown are several and can be associated with the existence of spots on the stellar surface, variations in circumstellar extinction, or changes in the geometry of an accretion disc. Using variability, a new population of objects has been uncovered that is believed to be part of the Rho Ophiuchi cluster.
We report here the discovery of a 30"-chain of embedded Herbig-Haro (HH) objects in the rho Ophiuchi dark cloud. These HH objects were first detected during a deep K_S-band observation (completeness magnitude for point source~19) made with NTT/SOFI. We confirm their nature with follow-up observations made with H_2 v=1-0 S(1) narrow-band filter. We argue that they belong to two different jets emanating from two Class I protostars: the main component of the recently resolved subarcsecond radio binary YLW15 (also called IRS43), and IRS54. We propose also to identify the [S II] knot HH224NW1 (Gome…
We present a volume-limited multiplicity survey with magnitude cutoff (K =< 10.5 mag) of 158 young stellar objects located within or in the vicinity of the Rho Ophiuchi Dark Cloud. With exception of eleven already well observed objects, all sources have been observed by us in the K-band with 3.5m telescopes by using speckle techniques. The separation range covered by our survey is [0.13'',6.4''], where the lower limit is given by the diffraction limit of the telescopes and the upper limit by confusion with background stars. The multiplicity survey is complete for flux ratios => 0.1 (=< 2.5 mag…
A review of star formation in the Rho Ophiuchi molecular complex is presented, with particular emphasis on studies of the main cloud, L1688, since 1991. Recent photometric and parallax measurements of stars in the Upper Scorpius subgroup of the Sco-Cen OB association suggest a distance for the cloud between 120 and 140 parsecs. Star formation is ongoing in the dense cores of L1688 with a median age for young stellar objects of 0.3 Myr. The surface population appears to have a median age of 2-5 Myr and merges with low mass stars in the Upper Scorpius subgroup. Making use of the most recent X-ra…
I analyze unpublished or partially published archival ROSAT data of the rho Ophiuchi dark cloud. This set of seven overlapping ROSAT HRI pointings, composed of eight ~one-hour exposures, detects mainly the X-ray brightest T Tauri stars of this star-forming region. Only two HRI sources are new X-ray sources, and their optical counterparts are proposed as new Weak T Tauri star candidates. Meanwhile the ROSAT HRI caught during just one exposure a weak X-ray source (maximum likelihood=10; SNR=4.1σfor Gaussian statistics) among a group of three embedded young stellar objects including two Class I p…
The isotope ratio, 85Rb/87Rb, places constraints on models of the nucleosynthesis of heavy elements, but there is no precise determination of the ratio for material beyond the Solar System. We report the first measurement of the interstellar Rb isotope ratio. Our measurement of the Rb I line at 7800 A for the diffuse gas toward rho Oph A yields a value of 1.21 +/- 0.30 (1-sigma) that differs significantly from the meteoritic value of 2.59. The Rb/K elemental abundance ratio for the cloud also is lower than that seen in meteorites. Comparison of the 85Rb/K and 87Rb/K ratios with meteoritic valu…
The results of a near-infrared (J H K LP) imaging linear polarimetry survey of 20 young stellar objects (YSOs) in rho Ophiuchi are presented. The majority of the sources are unresolved, with K-band polarizations, P_K < 6 per cent. Several objects are associated with extended reflection nebulae. These objects have centrosymmetric vector patterns with polarization discs over their cores; maximum polarizations of P_K > 20 per cent are seen over their envelopes. Correlations are observed between the degree of core polarization and the evolutionary status inferred from the spectral energy distribut…
We present the results of the first extensive mid-infrared (IR) imaging survey of the rho Ophiuchi embedded cluster, performed with the ISOCAM camera on board the ISO satellite. The main molecular cloud L1688, as well as L1689N and L1689S, have been completely surveyed for point sources at 6.7 and 14.3 micron. A total of 425 sources are detected including 16 Class I, 123 Class II, and 77 Class III young stellar objects (YSOs). Essentially all of the mid-IR sources coincide with near-IR sources, but a large proportion of them are recognized for the first time as YSOs. Our dual-wavelength survey…
We present the Chandra ACIS and ASCA GIS results for a series of four long-term observations on DoAr 21, ROXs 21 and ROXs 31; the X-ray brightest T-Tauri stars (TTSs) in the Rho Ophiuchi cloud. In the four observations with a net exposure of ~600 ksec, we found six, three and two flares from DoAr 21, ROXs 21 and ROXs 31, respectively; hence the flare rate is fairly high. The spectra of DoAr 21 are well fitted with a single-temperature plasma model, while those of ROXs 21 and ROXs 31 need an additional soft plasma component. Since DoAr 21 is younger (~10^5 yr) than ROXs 21 and ROXs 31 (~10^6 yr…
We present new near- and mid-infrared observations of 19 Class I/flat-spectrum young stellar objects in the nearby Rho Oph (d=125pc) and Serpens (d=310pc) dark clouds. These observations are part of a larger systematic infrared multiplicity survey of Class I/flat-spectrum objects in the nearest dark clouds. We find 7/19 (37% +/- 14%) of the sources surveyed to be multiple systems over a separation range of ~150 - 1800 AU. This is consistent with the fraction of multiple systems found among older pre-main-sequence stars in each of the Taurus, Rho Oph, Chamaeleon, Lupus, and Corona Australis sta…
Errors were made in the calculations of EMs using the best fit normalizations in XSPEC. Lists of the errors and corrections are as follows. (1)Tables 1, 3, and 4 in ApJ, 557, 747 and astro-ph/0104190 (YSOs in Rho Oph): All the EMs in these tables should be multiplied by pi; the log(EM) in the first raw in Table 1, for example, is 52.6(52.2--53.2), not 52.1(51.7--52.7). (2)Figures 7 and 9 in ApJ, 557, 747 and astro-ph/0104190 (YSOs in Rho Oph): The EM plots should be systematically up-shifted by the factor of pi. (3)Table 3 in ApJ, 563, 361 and astro-ph/0108078 (young brown dwarfs in Rho Oph): …
We present the results of a radial velocity (RV) survey of 14 brown dwarfs (BDs) and very low-mass (VLM) stars in the Upper Scorpius OB association (UScoOB) and 3 BD candidates in the rho Ophiuchi dark cloud core. We obtained high-resolution echelle spectra at the Very Large Telescope using Ultraviolet and Visual Echelle Spectrograph (UVES) at two different epochs for each object, and measured the shifts in their RVs to identify candidates for binary/multiple systems in the sample. The average time separation of the RV measurements is 21.6d, and our survey is sensitive to the binaries with sep…
We present results of an X-ray search from bona-fide and candidate brown dwarfs in the Rho Ophiuchi cloud cores with the Chandra X-ray Observatory. The selected areas are two fields near the cloud center and are observed with the ACIS-I array of a 17'x17' size and a ~100 ks exposure. Among 18 bona-fide and candidate brown dwarfs listed by the infrared spectroscopy, we find X-ray emission from 7 sources above 99.9% confidence level. Therefore ~40% of the infrared-selected brown dwarfs in this cloud emit X-rays. For the brightest 4 sources, the X-ray spectra are made and are fitted with a thin-t…
We present the results of optical spectroscopy of 139 stars obtained with the Hydra multi-object spectrograph. The objects extend over a 1.3 square degree area surrounding the main cloud of the rho Oph complex. The objects were selected from narrowband images to have H alpha in emission. Using the presence of strong H alpha emission, lithium absorption, location in the Hertzsprung-Russell diagram, or previously reported x-ray emission, we were able to identify 88 objects as young stars associated with the cloud. Strong H alpha emission was confirmed in 39 objects with line widths consistent wi…
Mass accretion rate determinations are fundamental for an understanding of the evolution of pre-main sequence star circumstellar disks. Magnetospheric accretion models are used to derive values of the mass accretion rates in objects of very different properties, from brown dwarfs to intermediate-mass stars; we test the validity of these models in the brown dwarf regime, where the stellar mass and luminosity, as well as the mass accretion rate, are much lower than in T Tauri stars. We have measured simultaneously two infrared hydrogen lines, Pab and Brg, in a sample of 16 objects in the star-fo…
We present a comprehensive study of the rho Ophiuchi molecular cloud that addresses aspects of the physical structure and condition of the molecular cloud and its photodissociation region (PDR) by combining far-infrared and submillimeter-wave observations with a wide range of angular scale and resolution. We present 40'x40' maps in CO(4-3) and [CI](3P1-3P0) line emission from the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO), and pointed observations in the CO(7-6) and [CI](3P2-3P1) lines. Within, smaller spectral line maps of the cloud in CO, CS, HCO+ and their rare isotop…
The rho Oph molecular cloud is undergoing intermediate-mass star formation. UV radiation from its hottest young stars heats and dissociates exposed layers, but does not ionize hydrogen. Only faint radiation from the Rayleigh-Jeans tail of ~10-100K dust is expected at wavelengths longwards of 3mm. Yet Cosmic Background Imager (CBI) observations reveal that the rho Oph W photo-dissociation region (PDR) is surprisingly bright at centimetre wavelengths. We searched for interpretations consistent with the WMAP radio spectrum, new ISO-LWS parallel mode images and archival Spitzer data. Dust-related …
We present an analysis of low resolution infrared spectra for 20 brown dwarf candidates in the core of the $ρ$ Ophiuchi molecular cloud. Fifteen of the sources display absorption-line spectra characteristic of late-type stars. By comparing the depths of water vapor absorption bands in our candidate objects with a grid of M dwarf standards, we derive spectral types which are independent of reddening. Optical spectroscopy of one brown dwarf candidate confirms the spectral type derived from the water bands. Combining their spectral types with published near-infrared photometry, effective temperat…
We report that the H_alpha emission line of RS Oph was strongly variable during our 2004 observations on a time scale of 1 month. The line consisted of both a double peaked central narrow component (FWHM ~ 220 km/s) and a strongly variable broad one (FWHM ~ 2000 km/s). The base of the H_alpha line was very broad with FWZI 4600 km/s on all spectra from 1986 to 2004. The variability of the broad component extends from -2000 to +2000 km/s. Most probably this is due to either blobs ejected from the white dwarf (with a typical blob mass estimated to be ~10^{-10} M_solar or a variable accretion disk…
Results of a comprehensive, new, ground-based mid-infrared imaging survey of the young stellar population of the Rho Ophiuchi cloud are presented. Data were acquired at the Palomar 5-m and at the Keck 10-m telescopes with the MIRLIN and LWS instruments, at 0.25 arcsec and 0.25 arcsec resolutions, respectively. Of 172 survey objects, 85 were detected. Among the 22 multiple systems observed, 15 were resolved and their individual component fluxes determined. A plot of the frequency distribution of the detected objects with SED spectral slope shows that YSOs spend ~400,000 yr in the Flat Spectrum …
We have obtained moderate-resolution (R=800-1200) K-band spectra for ~100 stars within and surrounding the cloud core of rho Oph. We have measured spectral types and continuum veilings and have combined this information with results from new deep imaging. The IMF peaks at about 0.4 M_sun and slowly declines to the hydrogen burning limit with a slope of ~-0.5 in logarithmic units (Salpeter is +1.35). Our lower limits on the numbers of substellar objects demonstrate that the IMF probably does not fall more steeply below the hydrogen burning limit, at least down to ~0.02 M_sun. We then make the f…
We present ISO-LWS measurements of the main gas cooling lines, C+ 158 mum and O 63 mum towards a moderate opacity molecular cloud (Av=3), L1721, illuminated by the B2 star nu Sco (X = 5-10). These data are combined with an extinction map and IRAS dust emission images to test our understanding of gas heating and cooling in photo-dissociation regions (PDRs). This nearby PDR is spatially resolved in the IRAS images; variations in the IRAS colors across the cloud indicate an enhanced abundance of small dust grains within the PDR. A spatial correlation between the gas cooling lines and the infrared…
We observed the main core F of the rho Ophiuchi cloud, an active star-forming region located at ~140 pc, using XMM-Newton with an exposure of 33 ks. We detect 87 X-ray sources within the 30' diameter field-of-view of the it EPIC imaging detector array. We cross-correlate the positions of XMM-Newton X-ray sources with previous X-ray and infrared (IR) catalogs: 25 previously unknown X-ray sources are found from our observation; 43 X-ray sources are detected by both XMM-Newton and Chandra; 68 XMM-Newton X-ray sources have 2MASS near-IR counterparts. We show that XMM-Newton and Chandra have compar…
We have performed a 1 square degree 1.2mm dust continuum survey in the rho Oph molecular cloud. We detect a number of previously unknown sources, ranging from extended cores over compact, starless cores to envelopes surrounding young stellar objects of Class 0, Class I, and Class II type. We analyse the mass distribution, spatial distribution and the potential equilibrium of the cores. For the inner regions, the survey results are consistent with the findings of previous narrower surveys. The core mass function resembles the stellar initial mass function, with the core mass function shifted by…
Molecular oxygen, O2 has been expected historically to be an abundant component of the chemical species in molecular clouds and, as such, an important coolant of the dense interstellar medium. However, a number of attempts from both ground and from space have failed to detect O2 emission. The work described here uses heterodyne spectroscopy from space to search for molecular oxygen in the interstellar medium. The Odin satellite carries a 1.1 m sub-millimeter dish and a dedicated 119 GHz receiver for the ground state line of O2. Starting in 2002, the star forming molecular cloud core rho Oph A …
We report on the results of a systematic study of X-ray flares from low-mass young stellar objects, using Chandra observations of the main region of the Rho Oph. From 195 X-ray sources, including class I-III sources and some young brown dwarfs, we detected a total of 71 X-ray flares. Most of the flares have the typical profile of solar and stellar flares, fast rise and slow decay. We derived the time-averaged temperature (kT), luminosity (L_X), rise and decay timescales (tau_r and tau_d) of the flares, finding that (1) class I-II sources tend to have a high kT, (2) the distribution of L_X duri…
We report the discovery in NIR with SofI at the NTT of a resolved circumstellar dust disk around a 2MASS source at the periphery of the rho Ophiuchi dark cloud. We present follow-up observations in J, H, and Ks-band obtained with ISAAC at the VLT, under 0.4"-seeing conditions, which unveil a dark dust lane oriented East-West between two characteristic northern and southern reflection nebulae. This new circumstellar dust disk has a radius of 2.15" (300 AU at 140 pc), and a width of 1.2" (170 AU at 140 pc). Thanks to its location at the periphery of the dense cores, it suffers small foreground v…
We have carried out a new, near-infrared speckle imaging survey of 19 members of the young stellar population in the nearby (d=140 pc), Rho Ophiuchi cloud core. Results for four binary and one newly discovered triple system are reported. Data for all known multiple systems among the pre-main-sequence population of Rho Oph are tabulated. We define a "restricted binary fraction", Fbr, and a "restricted companion fraction", Fcr, as counting only those systems most detectable in the present and previous high-resolution near-infrared imaging surveys, having separations between 0.1-1.1 arcsec and K-…
We initiated digitization of the Moscow collection of astronomical plates using flatbed scanners. Techniques of photographic photometry of the digital images were applied, enabling an effective search for new variable stars. Our search for new variables among 140000 stars in the 10 x 5 degrees northern half of the field centered at 66 Oph, photographed with the Sternberg Institute's 40-cm astrograph in 1976--1995, gave 274 new discoveries, among them: 2 probable Population II Cepheids; 81 eclipsing variables; 5 high-amplitude Delta Scuti stars (HADSs); 82 RR Lyr stars; 62 red irregular variabl…
We present an analysis of ground-based optical photometry and spectroscopy, and Rossi X-ray Timing Explorer X-ray observations of the old novae DI Lacertae and V841 Ophiuchi. Our optical photometry data (obtained with the automated photometry telescope RoboScope) comprise an almost decade-long light curve for each star, while the contemporaneous spectroscopy and X-ray observations repeatedly sampled each nova during separate intervals of ~45-55 d in length. The long-term optical light curves of both novae reveal quasiperiodic variability on typical time scales of ~30-50 d with amplitudes of dV…
We present submillimetre data for the L1689 cloud in the rho-Ophiuchi molecular cloud complex. We detect a number of starless and prestellar cores and protostellar envelopes. We also detect a number of filaments for the first time in the submillimetre continuum that are parallel both to each other, and to filaments observed in the neighbouring L1688 cloud. These filaments are also seen in the 13CO observations of L1689. The filaments contain all of the star-formation activity in the cloud. L1689 lies next to the well studied L1688 cloud that contains the rho Oph-A core. L1688 has a much more a…
Observations of the rho Ophiuchi star forming region with VLT ANTU and ISAAC under 0.35" seeing conditions reveal two bipolar reflection nebulosities intersected by central dust lanes. The sources (OphE-MM3 and CRBR 2422.8-3423) can be identified as spatially resolved circumstellar disks viewed close to edge-on, similar to edge-on disk sources discovered previously in the Taurus and Orion star forming regions. Millimeter continuum fluxes yield disk masses of the order of 0.01 Mo, i.e. about the mass deemed necessary for the minimum solar nebula. Follow-up spectroscopic observations with SUBARU…
We report the results of long observing campaigns on two novalike variables: V442 Ophiuchi and RX J1643.7+3402. These stars have high-excitation spectra, complex line profiles signifying mass loss at particular orbital phases, and similar orbital periods (respectively 0.12433 and 0.12056 d). They are well-credentialed members of the SW Sex class of cataclysmic variables. Their light curves are also quite complex. V442 Oph shows periodic signals with periods of 0.12090(8) and 4.37(15) days, and RX J1643.7+3402 shows similar signals at 0.11696(8) d and 4.05(12) d. We interpret these short and lo…
We present new near-IR observations of 76 Class I/flat-spectrum objects in the nearby (d < 320 pc) Perseus, Taurus, Chamaeleon I and II, rho Ophiuchi, and Serpens dark clouds. These observations are part of a larger systematic infrared multiplicity survey of self-embedded objects in the nearest dark clouds. When combined with the results of our previously published near-infrared multiplicity survey, we find a restricted companion star fraction of 14/79 (18% +/- 4%) of the sources surveyed to be binary or higher order multiple systems over a separation range of ~300 - 2000 AU with a magnitude d…
This paper reviews the Chandra deep exposure observations of star forming regions, rho-Ophiuchi, Orion Molecular Clouds 2 and 3, Sagittarius B2 and Monoceros R2. The results are; (1) class I protostars are found to exhibit higher temperature plasma than those of T Tauri stars, (2) heavily absorbed X-rays are discovered from the candidates of class 0 protostars, (3) hard and highly variable X-rays are observed from high-mass young stars, and (4) young brown dwarfs emit X-rays similar to those of low-mass young stars.
We present a detailed X-ray study of the microquasar GRS 1915+105 during a variability class transition observed in 2000 June with the PPCs of the Indian X-ray Astronomy Experiment. We supplement this observation with data from the RXTE archives. The source made a transition from a steady low-hard state to a regular oscillatory behaviour in the light curve known as bursts or class `rho' (Belloni et al. 2000) between 2000 May 11 and 17 and reverted back to the low-hard state on 2000 June 27. A gradual change in the burst recurrence time from about 75 s to about 40 s was observed which then incr…
AIMS. We study the variability of the Fe 6.4 KeV emission line from the Class I young stellar object Elias 29 in the Rho-Oph cloud. METHODS. We analysed the data from Elias 29 collected by XMM during a nine-day, nearly continuous observation of the Rho-Oph star-forming region (the Deep Rho-Oph X-ray Observation, named Droxo). The data were subdivided into six homogeneous time intervals, and the six resulting spectra were individually analysed. RESULTS. We detect significant variability in the equivalent width of the Fe 6.4 keV emission line from Elias 29. The 6.4 keV line is absent during the …
In the summer and fall of 2000 the yellow hypergiant Rho Cassiopeiae dimmed by more than a visual magnitude, while its effective temperature decreased from \~7000 K to below 4000 K over ~200 d. We observed the highest mass-loss rate of ~5 % of the solar mass per year in a single stellar eruption so far (Lobel et al. 2003, ApJ, 583, 923). We determine from newly formed TiO bands a gas mass-loss rate of M_dot ~ 5.4 10^{-2} Msun/yr, which is of the same order of magnitude as has been proposed for the giant outbursts of the Luminous Blue Variable Eta Carinae. Over the past two years since the outb…
We present the results of a mid-infrared imaging spectroscopy survey of Young Stellar Objects (YSOs) and their surrounding environment in four low-mass star formation regions: RCrA, Rho Ophiuchi, Serpens and Chamaeleon I. This survey was performed using ISOCAM and its Circular Variable Filters (CVF) and observed 42 YSO candidates. A number of spectral features were measured, most notably the 9.7um silicate feature, the bending modes of both water and CO2 ices at 6.0 and 15.2um respectively and the well-known unidentified feature at 6.8um. The strength of the unidentified feature was observed t…
We present results from an ISOCAM survey in the two broad band filters LW2 (5-8.5 mu) and LW3 (12-18 mu) 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 band and 139 in the 14.3 mu band to a limiting sensitivity of ~ 2 mJy. Only about 50% of the mid-IR excess sources show excesses in the near-IR J-H/H-K diagram. In the central Cloud Core the Class I/Class II number ratio is 19/18, i.e. about 10 times larger than in other young embedded clusters such as rho Ophiuchi or Chamaeleon. The mid-IR fluxes of the Class I and flat-spect…
Embedded clusters usually contain young stellar objects in different evolutionary stages. We investigate number ratios of objects in these classes in the star-forming regions rho Ophiuchi, Serpens, Taurus, Chamaeleon I, NGC 7129, IC 1396A, and IC 348. They are compared to the temporal evolution of young stars in numerical simulations of gravoturbulent fragmentation in order to constrain the models and to possibly determine the evolutionary stage of the clusters. It turns out that Serpens is the youngest, and IC 348 the most evolved cluster, although the time when the observations are best repr…
We present an overview of the spectral variability of the peculiar F-type hypergiant Rho Cas, obtained from our long-term monitoring campaigns over the past 8.5 years with four spectrographs in the northern hemisphere. Between 2000 June and September an exceptional variability phase occurred when the V-brightness dimmed by about a full magnitude. The star recovered from this deep minimum by 2001 April. It is the third outburst of Rho Cas on record in the last century. We observe TiO absorption bands in high-resolution near-IR spectra obtained with the Utrecht Echelle Spectrograph during the su…
Recent observations suggest that mass ejection and mass accretion both decline significantly with time during early protostellar evolution (Bontemps et al. 1996). In the present paper, we propose that this rapid decay of accretion/ejection activity is a direct result of the non-singular density profiles characterizing pre-collapse clouds. The radial density profiles of pre-stellar cores are indeed found to be much flatter than rho(r) ~ r(-2) at radii less than a few thousand AU (Ward-Thompson et al. 1994). Here we show, through Lagrangian analytical calculations, that the supersonic gravitatio…
We have carried out a survey of optically-selected dark clouds using the bolometer array SCUBA on the James Clerk Maxwell Telescope, at 850 microns wavelength. The survey covers a total of 0.5 square degrees and is unbiased with reference to cloud size, star formation activity, or the presence of infrared emission. Several new protostars and starless cores have been discovered; the protostars are confirmed through the detection of their accompanying outflows in CO(2-1) emission. The survey is believed to be complete for Class 0 and Class I protostars, and yields two important results regarding…
We have obtained two deep exposures of the rho Oph cloud core region with the ROSAT HRI. The improved position accuracy (1"-6") with respect to previous recent X-ray observations (ROSAT PSPC, and ASCA) allows us to remove positional ambiguities for the detected sources. We also cross-correlate the X-ray positions with IR sources found in the ISO-ISOCAM survey of the same region at 6.7 and 14.3 \mum, in addition to sources known from ground-based observations, which are young stars. We find that there is no statistically significant difference between the X-ray luminosity functions of HRI-detec…
We present high resolution (R=50,000) spectra at 2.2 um of 16 young stars in the rho Ophiuchi dark cloud. Photospheric features are detected in the spectra of 11 of these sources, all Class II young stellar objects. In 10 of these sources, we measure effective temperatures, continuum veiling, and vsini rotation from the shapes and strengths of atomic photospheric lines by comparing to spectral synthesis models at 2.2 um. We measure surface gravities in 2 stars from the integrated line flux ratio of the 12CO line region at 2.3 um and the Na I line region at 2.2 um. Although the majority (8/10) …
We have analyzed photometric and spectroscopic data of a sample of 14 spatially resolved pre-main-sequence binaries (separations 0.6" to 1.7") in the nearby (150 pc) low-mass star-forming regions of Chamaeleon, Lupus, and rho Ophiuchi. The spectroscopic data have been obtained with the ESO New Technology Telescope (NTT) at La Silla under subarcsec seeing conditions. All binaries (originally unresolved) were identified as pre-main-sequence stars based on their strong H-alpha emission -- which classifies them as classical T Tauri stars -- and their association with dark clouds. One of the presum…
(abbreviated) We aim to determine the masses of the envelopes, disks, and central stars of young stellar objects (YSOs) in the Class I stage. We observed the embedded Class I objects IRS 63 and Elias 29 in the rho Ophiuchi star-forming region with the Submillimeter Array (SMA) at 1.1 mm. IRS 63 and Elias 29 are both clearly detected in the continuum, with peak fluxes of 459 resp. 47 mJy/beam. The continuum emission toward Elias 29 is clearly resolved, whereas IRS 63 is consistent with a point source down to a scale of 3 arcsec (400 AU). The SMA data are combined with single-dish data, and disk…
Medium resolution (lambda/Delta lambda = 5000-10000) VLT-ISAAC M-band spectra are presented of 39 young stellar objects in nearby low-mass star forming clouds showing the 4.67 micron stretching vibration mode of solid CO. By taking advantage of the unprecedentedly large sample, high S/N ratio and high spectral resolution, similarities in the ice profiles from source to source are identified. It is found that excellent fits to all the spectra can be obtained using a phenomenological decomposition of the CO stretching vibration profile at 4.67 micron into 3 components. All observed interstellar …
Spectra of B stars in the wavelength range of 911-1100 A have been obtained with the EURD spectrograph onboard the Spanish satellite MINISAT-01 with ~5 A spectral resolution. IUE spectra of the same stars have been used to normalize Kurucz models to the distance, reddening and spectral type of the corresponding star. The comparison of 8 main-sequence stars studied in detail (alpha Vir, epsilon Tau, lambda Tau, tau Tau, alpha Leo, zeta Lib, theta Oph, and sigma Sgr) shows agreement with Kurucz models, but observed fluxes are 10-40% higher than the models in most cases. The difference in flux be…
