We present a catalogue of Molecular Hydrogen emission-line Objects (MHOs) in outflows from young stars, most of which are deeply embedded. All objects are identified in the near-infrared lines of molecular hydrogen, all reside in the Milky Way, and all are associated with jets or molecular outflows. Objects in both low and high-mass star forming regions are included. This catalogue complements the existing database of Herbig-Haro objects; indeed, for completeness, HH objects that are detected in H_2_ emission are included in the MHO catalogue.
We present the analysis of 35.5deg^2^ of images in the 1-0 S(1) line of H_2_ from the UK Widefield Infrared Survey for H_2_ (UWISH2) towards Cassiopeia and Auriga. We have identified 98 Molecular Hydrogen emission-line Objects (MHOs) driven by Young Stellar Objects, 60 per cent of which are bipolar outflows and all are new discoveries. We estimate that the UWISH2-extended emission object catalogue contains fewer than 2 per cent false positives and is complete at the 95 per cent level for jets and outflows brighter than the UWISH2 detection limit. We identified reliable driving source candidates for three quarters of the detected outflows, 40 per cent of which are associated with groups and clusters of stars. The driving source candidates are 20 per cent protostars, the remainder are Classical T-Tauri Stars. We also identified 15 new star cluster candidates near MHOs in the survey area. We find that the typical outflow identified in the sample has the following characteristics: the position angles are randomly orientated; bipolar outflows are straight within a few degrees; the two lobes are slightly asymmetrical in length and brightness; the length and brightness of the lobes are not correlated; typical time gaps between major ejections of material are 1-3 kyr, hence FU-Ori or EX-Ori eruptions are most likely not the cause of these, but we suggest MNors as a possible source. Furthermore, we find that outflow lobe length distributions are statistically different from the widely used total length distributions. There are a larger than expected number of bright outflows indicating that the flux distribution does not follow a power law.
Jets and outflows from young stellar objects (YSOs) are important signposts of currently ongoing star formation. In order to study these objects, we are conducting an unbiased survey along the Galactic plane in the 1-0 S(1) emission line of molecular hydrogen at 2.122 um using the United Kingdom Infrared Telescope. In this paper, we are focusing on a 33-deg^2^-sized region in Serpens and Aquila (18{deg}<l<30{deg}; -1.5{deg}<b<+1.5{deg}). We trace 131 jets and outflows from YSOs, which results in a 15-fold increase in the total number of known molecular hydrogen outflows. Compared to this, the total integrated 1-0 S(1) flux of all objects just about doubles, since the known objects occupy the bright end of the flux distribution. Our completeness limit is 3x10^-18^W/m^2^ with 70 per cent of the objects having fluxes of less than 10^-17^W/m^2^.
We present the results of a narrow-band near-infrared imaging survey for Molecular Hydrogen emission-line Objects (MHOs) toward 26 regions containing high-mass protostellar candidates and massive molecular outflows. We have detected a total of 236 MHOs, 156 of which are new detections, in 22 out of the 26 regions. We use H_2_2.12{mu}m/H_2_2.25{mu}m flux ratios, together with morphology, to separate the signatures of fluorescence associated with photo- dissociation regions (PDRs) from shocks associated with outflows in order to identify the MHOs. PDRs have typical low flux ratios of ~1.5-3, while the vast majority of MHOs display flux ratios typical of C-type shocks (~6-20). A few MHOs exhibit flux ratios consistent with expected values for J-type shocks (~3-4), but these are located in regions that may be contaminated with fluorescent emission. Some previously reported MHOs have low flux ratios, and are likely parts of PDRs rather than shocks indicative of outflows. We identify a total of 36 outflows across the 22 target regions where MHOs were detected. In over half these regions, MHO arrangements and fluorescent structures trace features present in CO outflow maps, suggesting that the CO emission traces a combination of dynamical effects, which may include gas entrained in expanding PDRs as well as bipolar outflows. Where possible, we link MHO complexes to distinct outflows and identify candidate driving sources.
Protoplanetary disks show large diversity regarding their morphology and dust composition. With mid-infrared interferometry the thermal emission of disks can be spatially resolved, and the distribution and properties of the dust within can be studied. Our aim is to perform a statistical analysis on a large sample of 82 disks around low- and intermediate-mass young stars, based on mid-infrared interferometric observations. We intend to study the distribution of disk sizes, variability, and the silicate dust mineralogy. Archival mid-infrared interferometric data from the MIDI instrument on the Very Large Telescope Interferometer are homogeneously reduced and calibrated. Geometric disk models are used to fit the observations to get spatial information about the disks. An automatic spectral decomposition pipeline is applied to analyze the shape of the silicate feature. We present the resulting data products in the form of an atlas, containing N band correlated and total spectra, visibilities, and differential phases. The majority of our data can be well fitted with a continuous disk model, except for a few objects, where a gapped model gives a better match. From the mid-infrared size-luminosity relation we find that disks around T Tauri stars are generally colder and more extended with respect to the stellar luminosity than disks around Herbig Ae stars. We find that in the innermost part of the disks (r<~1au) the silicate feature is generally weaker than in the outer parts, suggesting that in the inner parts the dust is substantially more processed. We analyze stellar multiplicity and find that in two systems (AB Aur and HD 72106) data suggest a new companion or asymmetric inner disk structure. We make predictions for the observability of our objects with the upcoming Multi-AperTure mid- Infrared SpectroScopic Experiment (MATISSE) instrument, supporting the practical preparations of future MATISSE observations of T Tauri stars.
An infrared study that includes ground-based mid-infrared images between 8.7 and 18.7um and IRAC images at 3.6, 4.5, 5.8 and 8.0um of the W75 N massive star forming region is presented. The 12.5um image shows the presence of four mid-infrared sources in the region W75 N(B), three of which have bright near-infrared counterparts, IRS 1, IRS 2 and IRS 3, all with significant excess emission at lambda>2.0um. IRS 2 has a steep energy distribution and the computed infrared luminosity is consistent with the presence of a young B3 star. The observed IRAC colors of IRS 3 indicate that this source is a Class II intermediate mass young star, consistent with its infrared energy distribution and luminosity. The fourth, newly discovered, mid-infrared source appears coincident with the ultracompact HII region VLA 3, and is located within the millimeter core MM 1. We derived a luminosity of ~750L_{sun}_ and a visual extinction A_V_~90 for this source. From the IRAC images, we detected 75 sources in an area of 120"x120" centered in W75 N. At least 25 of these sources are associated with the molecular cloud and form a young stellar cluster as shown in the IRAC two-color and the H-Ks versus Ks-[3.6] diagrams.
We present initial results from time-series imaging at infrared wavelengths of 0.9deg^2^ in the Orion Nebula Cluster (ONC). During Fall 2009 we obtained 81 epochs of Spitzer 3.6 and 4.5um data over 40 consecutive days. We extracted light curves with ~3% photometric accuracy for ~2000 ONC members ranging from several solar masses down to well below the hydrogen-burning mass limit. For many of the stars, we also have time-series photometry obtained at optical (Ic) and/or near-infrared (JKs) wavelengths. Our data set can be mined to determine stellar rotation periods, identify new pre-main-sequence eclipsing binaries, search for new substellar Orion members, and help better determine the frequency of circumstellar disks as a function of stellar mass in the ONC. Our primary focus is the unique ability of 3.6 and 4.5um variability information to improve our understanding of inner disk processes and structure in the Class I and II young stellar objects (YSOs). In this paper, we provide a brief overview of the YSOVAR Orion data obtained in Fall 2009 and highlight our light curves for AA-Tau analogs -YSOs with narrow dips in flux, most probably due to disk density structures passing through our line of sight. Detailed follow-up observations are needed in order to better quantify the nature of the obscuring bodies and what this implies for the structure of the inner disks of YSOs.
We have used Spitzer/Infrared Array Camera (IRAC) to conduct a photometric monitoring program of the IC1396A dark globule in order to study the mid-IR (3.6-8um) variability of the heavily embedded young stellar objects (YSOs) present in that area. We obtained light curves covering a 14 day timespan with a twice daily cadence for 69 YSOs, and continuous light curves with approximately 12s cadence over 7hr for 38 YSOs. Typical accuracies for our relative photometry were 1%-2% for the long timespan data and a few millimagnitude, corresponding to less than 0.5%, for the 7hr continuous "staring-mode" data. More than half of the YSOs showed detectable variability, with amplitudes from ~0.05mag to ~0.2mag. One star, IC1396A-47, shows a 3.5hr periodic light curve; this object may be a PMS Delta Scuti star.
Mineralogical studies of silicate features emitted by dust grains in protoplanetary disks and solar system bodies can shed light on the progress of planet formation. The significant fraction of crystalline material in comets, chondritic meteorites, and interplanetary dust particles indicates a modification of the almost completely amorphous interstellar medium dust from which they formed. The production of crystalline silicates, thus, must happen in protoplanetary disks, where dust evolves to build planets and planetesimals. Different scenarios have been proposed, but it is still unclear how and when this happens. This paper presents dust grain mineralogy (composition, crystallinity, and grain size distribution) of a complete sample of protoplanetary disks in the young Serpens cluster. These results are compared to those in the young Taurus region and to sources that have retained their protoplanetary disks in the older Upper Scorpius and {eta} Chamaeleontis stellar clusters, using the same analysis technique for all samples. This comparison allows an investigation of the grain mineralogy evolution with time for a total sample of 139 disks. The mean cluster age and disk fraction are used as indicators of the evolutionary stage of the different populations. Our results show that the disks in the different regions have similar distributions of mean grain sizes and crystallinity fractions (~10%-20%) despite the spread in mean ages. Furthermore, there is no evidence of preferential grain sizes for any given disk geometry nor for the mean cluster crystallinity fraction to increase with mean age in the 1-8Myr range. The main implication is that a modest level of crystallinity is established in the disk surface early on (<=1Myr), reaching an equilibrium that is independent of what may be happening in the disk midplane. These results are discussed in the context of planet formation, in comparison with mineralogical results from small bodies in our own solar system.
We present an HCO^+^ J=3->2 survey of Class 0+I and Flat SED young stellar objects (YSOs) found in the Gould Belt clouds by surveys with Spitzer. Our goal is to provide a uniform Stage 0+I source indicator for these embedded protostar candidates. We made single point HCO^+^ J=3->2 measurements toward the source positions at the CSO and APEX of 546 YSOs (89% of the Class 0+I + Flat SED sample). Using the criteria from van Kempen et al. (2009, J/A+A/498/167), we classify sources as Stage 0+I or bona fide protostars and find that 84% of detected sources meet the criteria. We recommend a timescale for the evolution of Stage 0+I (embedded protostars) of 0.54Myr. We find significant correlations of HCO^+^ integrated intensity with {alpha} and T_bol_ but not with L_bol_. The detection fraction increases smoothly as a function of {alpha} and L_bol_, while decreasing smoothly with T_bol_. Using the Stage 0+I sources tightens the relation between protostars and high extinction regions of the cloud; 89% of Stage I sources lie in regions with A_V_>8mag. Class 0+I and Flat SED YSOs that are not detected in HCO^+^ have, on average, a factor of ~2 higher T_bol_ and a factor of ~5 lower L_bol_than YSOs with HCO^+^ detections. We find less YSO contamination, defined as the number of undetected YSOs divided by the total number surveyed, for sources with T_bol_<~600K and L_bol_>~1L_{sun}_. The contamination percentage is >90% at A_V_<4mag and decreases as A_V_ increases.
