Joaquin Bohigas

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.

Photoionization Models Applied to Planetary Nebulae

Good to excellent photoionization models based on the Cloudy code (from Ferland and coworkers) were obtained for 13 out of 19 spectra of planetary nebulae (PNs). Results are deficient when the slit is missing most of the in-depth extent of the ionized region. Features that can be associated to shock excitation and abnormally large helium abundances are found when this is the case. Models assume that the exciting star is a Rauch photosphere illuminating a static uniform density spherical shell. Model central stars lie close to a 2.5 M? post-AGB theoretical evolutionary track in the H-R diagram (from Vassiliadis and Wood), with implied PN ages between 1000 and 7000 yr. Observed and modeled nebular temperatures derived from [N II] -->? ? (6548 + 6584)/? 5755 agree within 10%, but models usually underestimate temperatures found from [O III] -->? ? (4959 + 5007)/? 4363, more so when the slit does not cover the in-depth extent of the ionized region. Helium, nitrogen, oxygen, neon, sulfur, chlorine, and argon model abundances are uncertain at the 15%, 15%, 10%, 7%, 30%, 5%, and 7% levels, respectively. The following relationships between chemical elements are found: He tends to be more abundant when N/O is large; there is a loose anticorrelation between N/O and O/H; N/C and C/H are anticorrelated; and the sum of the carbon, nitrogen, and oxygen abundances is larger in carbon-rich objects. Finally, it is shown that neon abundance in PNs has been overestimated, and an alternative ionization correction factor is provided.

Dual infrared camera for near and mid infrared observations

We present the dual IR camera CID for the 2.12 m telescope of the Observatorio Astronomico Nacional de Mexico, IA-UNAM. The system consists of two separate cameras/spectrographs that operate in different regions of the IR spectrum. In the near IR, CID comprises a direct imaging camera with wide band filters, a CVF, and a low resolution spectrograph employing an InSb 256 x 256 detector. In the mid IR, CID uses a BIB 128 x 128 detector for direct imaging in 10 and 20 microns. Optics and mechanics of CID were developed at IR-Labs (Tucson). The electronics was developed by R. Leach (S. Diego). General design, construction of auxiliary optics (oscillating secondary mirror), necessary modifications and optimization of the electronics, and acquisition software were carried out at OAN/ UNAM. The compact design of the instruments allow them to share a single dewar and the cryogenics system.

Young Stellar Objects in Gy 2-18 (IRAS 05439+3035)

We present the results of optical and near-IR spectra and mid-infrared images of the star forming region Gy 2-18, which is associated with IRAS 05439+3035. Within this region, there is a star with strong Hα emission that is illuminating an optical reflection nebula. Optical and near-IR spectra indicate that this star, named IRS 11, is a possible Herbig Be star of spectral type BO–B2, with a strong stellar wind and an infrared excess probably originating in a circumstellar dust disk. The mid-infrared images at 8.7, 9.7, and 12.5 μm show the presence of a second very red source, IRS 9, deeply embedded in the cloud and with a remarkably strong silicate feature in absorption. The estimated bolometric luminosity of 8.6 × 103 L⊙ and the infrared spectral index αIR = 1.9 suggest that IRS 9 is a massive protostellar object. These two sources form the core of the young stellar cluster associated with Gy 2-18. The infrared luminosity and spectral index of another member, IRS 13, are estimated to be ≤165 L⊙ and ≤0.44.