M. Tapia

Hipparcos, VLA, and CCD Observations of Cygnus OB2 No. 5: Solving the Mysteryof the Radio “Companion”

We present accurate optical and radio astrometry for the unresolved contact binary system Cyg OB2 No. 5 and its weaker component to the northeast. While the radio and optical positions of the primary component (taken to be the unresolved contact binary) agree within observational error (~70 mas), we find that the weaker radio component does not agree in position with the second optical component of the system, but falls in between the two optical components. We conclude that the weaker radio component of this system is not associated with the secondary star but appears to be synchrotron emission produced at the shock interaction zone between the winds of the stars. Differential B- and V-band CCD and Hipparcos photometry was used to derive the approximate spectral type (B0 V-B2 V) of the secondary. Ram pressure arguments in the colliding-wind model give a mass-loss rate for the secondary star consistent with the expected one, considering the earliest spectral type.

Episodic dust formation by HD 192641 (WR 137) – II

Observations of the dust and gas around embedded stellar clusters reveal some of the processes involved in their formation and evolution. Large scale mass infall with rates dM/dt=4e-4 solar masses/year is found to be disrupted on small scales by protostellar outflows. Observations of the size and velocity dispersion of clusters suggest that protostellar migration from their birthplace begins at very early times and is a potentially useful evolutionary indicator.

Mid-infrared images of the massive star forming region W75 N

An infrared study that includes ground-based mid-infrared images between 8.7 and 18.7 μm and IRAC images at 3.6, 4.5, 5.8 and 8.0 μm of the W75 N massive star forming region is presented. The 12.5 μm 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 A > 2.0 μm. 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 ∼750 L ○. and a visual extinction A v ≃ 90 for this source. From the IRAC images, we detected 75 sources in an area of 120 x 120 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 - K s versus K s - [3.6] diagrams.

STAR FORMATION ACROSS THE W3 COMPLEX

We present a multi-wavelength analysis of the history of star formation in the W3 complex. Using deep, near-infrared ground-based images, combined with images obtained with Spitzer and Chandra observatories, we identified and classified young embedded sources. We identified the principal clusters in the complex, and determined their structure and extension. We constructed extinction-limited samples for five principal clusters, and constructed K-band luminosity functions (KLF) that we compare with those of artificial clusters with varying ages. This analysis provided mean ages and possible age spreads for the clusters. We found that IC 1795, the centermost cluster of the complex, still hosts a large fraction of young sources with circumstellar disks. This indicates that star formation was active in IC 1795 as recently as 2 Myr ago, simultaneous to the star forming activity in the flanking embedded clusters, W3-Main and W3(OH). A comparison with carbon monoxide emission maps indicates strong velocity gradients in the gas clumps hosting W3-Main and W3(OH) and show small receding clumps of gas at IC 1795, suggestive of rapid gas removal (faster than the T Tauri timescale) in the cluster forming regions. We discuss one possible scenario for the progression of cluster formation in the W3 complex. We propose that early processes of gas collapse in the main structure of the complex could have defined the progression of cluster formation across the complex with relatively small age differences from one group to another. However, triggering effects could act as catalysts for enhanced efficiency of formation at a local level, in agreement with previous studies.

Sh 2-128: An H II and Star-forming Region in the Galactic Outback

Near-infrared imaging photometry supplemented by optical spectroscopy and narrowband imaging of the H II region Sh 2-128 and its environment are presented. This region contains a developed H II region and a neighboring compact H II region associated with a pair of water maser sources. Midway between these, the core of a CO cloud is located. The principal ionizing source of Sh 2-128 is an O7 star close to its center. Slit spectroscopy was used to obtain nebular line fluxes, abundances, and the physical parameters of Sh 2-128. This H II region is optically thin from the optical to the radio and appears to be ionization-bounded. The present JHKs images show the presence of a number of point sources and nebular emission knots with large near-infrared excesses in the northern Sh 2-128N. One of the three red Ks knots coincides with the compact H II region. A few of the infrared-excess objects are close to known mid- and far-infrared emission peaks. Star counts in J and Ks show the presence of a small cluster of B-type stars, mainly associated with Sh 2-128N. Except for the youngest, reddest objects, the stars in the whole region are moderately obscured. The JHKs photometric properties, together with the characteristics of the other objects in the vicinity, suggest that Sh 2-128 and Sh 2-128N constitute a single complex formed from the same molecular cloud but with ages ~106 and less than 3 × 105 yr, respectively. A new spectroscopic distance of 9.4 kpc is derived. This implies a galactocentric distance of 13.5 kpc and z = 550. No molecular hydrogen emission was detected at 2.12 μm from any part of the surveyed region.

Spitzer IRAC Color Diagnostics for Extended Emission in Star Forming Regions

The infrared data from the Spitzer Space Telescope has provided an invaluable tool for identifying physical processes in star formation. In this study we calculate the IRAC color space of UV fluorescent molecular hydrogen (H

The enigmatic brown dwarf candidate [KG2001] 102 in the Chamaeleon I cloud: Is it a multiple system?

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The new star forming site NGC 6334 IV (MM3)

) and Polycyclic Aromatic Hydrocarbon (PAH) emission in photodissociation regions (PDRs) using the Cloudy code with PAH opacities from Draine & Li 2007. We create a set of color diagnostics that can be applied to study the structure of PDRs and to distinguish between FUV excited and shock excited H

STELLAR WIND FROM Of STARS FROM INFRARED AND RADIO OBSERVATIONS

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H2 shocks and mass accretion rate in high mass young stellar objects (HMYSOs)

emission. To test this method we apply these diagnostics to Spitzer IRAC data of NGC 2316. Our analysis of the structure of the PDR is consistent with previous studies of the region. In addition to UV excited emission, we identify shocked gas that may be part of an outflow originating from the cluster.