Wheels of Fire IV. Star Formation and the Neutral Interstellar Medium in the Ring Galaxy AM0644-741

We combine data from the ATNF and the SEST to investigate the neutral ISM in AM0644-741, a large and robustly star-forming ring galaxy. The galaxy's ISM is concentrated in the 42-kpc diameter starburst ring, but appears dominated by atomic gas, with a global molecular fraction (f_mol) of only 7.9%. Apart from the starburst peak, the gas ring is stable against the growth of gravitational instabilities (Q_gas=2-7). Including stars lowers Q overall, but not enough to make Q<1 everywhere. The ring's global star formation efficiency (SFE) appears somewhat elevated, but varies around the ring by more than an order of magnitude, peaking where star formation is most intense. AM0644-741's star formation law is peculiar: HI follows a Schmidt law while H2 is uncorrelated with SFR/area. Photodissociation models yield low volume densities in the ring, particularly in the starburst quadrant (n~2 cm^-3), implying a warm neutral medium dominated ISM. At the same time, the ring's pressure and ambient far-ultraviolet radiation field lead to the expectation of a predominantly molecular ISM. We argue that the ring's peculiar star formation law, n, SFE, and f_mol result from the ISM's >100 Myr confinement time in the starburst ring, which enhances the destructive effects of embedded massive stars and supernovae. As a result, the ring's molecular ISM becomes dominated by small clouds where star formation is most intense, causing H2 to be underestimated by 12CO line fluxes: in effect X(CO) >> X(Gal) despite the ring's solar metallicity. The observed large HI component is primarily a low density photodissociation product, i.e., a tracer rather than a precursor of massive star formation. Such an "over-cooked" ISM may be a general characteristic of evolved starburst ring galaxies.Comment: 41 pages, 7 tables, 18 eps figure

New binaries among UV-selected, hot subdwarf stars and population properties

We have measured the orbital parameters of seven close binaries, including six new objects, in a radial velocity survey of 38 objects comprising a hot subdwarf star with orbital periods ranging from ~0.17 to 3 d. One new system, GALEX J2205-3141, shows reflection on an M dwarf companion. Three other objects show significant short-period variations, but their orbital parameters could not be constrained. Two systems comprising a hot subdwarf paired with a bright main-sequence/giant companion display short-period photometric variations possibly due to irradiation or stellar activity and are also short-period candidates. All except two candidates were drawn from a selection of subluminous stars in the Galaxy Evolution Explorer ultraviolet sky survey. Our new identifications also include a low-mass subdwarf B star and likely progenitor of a low-mass white dwarf (GALEX J0805-1058) paired with an unseen, possibly substellar, companion. The mass functions of the newly identified binaries imply minimum secondary masses ranging from 0.03 to 0.39M?. Photometric time series suggest that, apart from GALEX J0805-1058 and J2205-3141, the companions are most likely white dwarfs. We update the binary population statistics: close to 40 per cent of hot subdwarfs have a companion. Also, we found that the secondary mass distribution shows a lowmass peak attributed to late-type dwarfs, and a higher mass peak and tail distribution attributed to white dwarfs and a few spectroscopic composites. Also, we found that the population kinematics imply an old age and include a few likely halo population members

Sentinel lymph node biopsy for conjunctival malignant melanoma: surgical techniques

Alberto JA Wainstein,1,2 Ana P Drummond-Lage,1 Milhem JM Kansaon,2 Gustavo O Bretas,2 Rodrigo F Almeida,3 Ana LF Gloria,3 Ana RP Figueiredo3 1Faculty of Medical Sciences of Minas Gerais, 2Oncad Surgical Oncology, 3Ophthalmology Department, Federal University of Minas Gerais, Belo Horizonte, Brazil Background: The purpose of this report is to examine the viability and safety of preoperative lymphoscintigraphy and radio guided sentinel lymph node (SLN) biopsy for conjunctival melanoma, and to identify the best technique to perform this procedure.Methods: Three patients diagnosed with malignant melanoma of the conjunctiva underwent lymphoscintigraphy and SLN biopsy using a dual technique comprising isosulfan blue dye and technetium Tc 99m sulfur colloid. Each patient was anesthetized and the conjunctival melanoma was excised. SLNs were localized by a gamma probe, identified according to radioactivity and sentinel blue printing, and dissected, along with drainage of the associated lymphatic basins. The SLNs were evaluated by a pathologist using hematoxylin-eosin staining following serial sectioning and immunohistochemistry using a triple melanoma cocktail (S-100, Melan-A, and HMB-45 antigens).Results: Two SLNs were stained in the jugular chain during preoperative lymphoscintigraphy in the first patient, two SLNs were identified in the preauricular and submandibular areas in the second patient, and two SLNs were identified in the submandibular and parotid areas in the third patient. All lymph nodes identified by lymphoscintigraphy were dissected and identified at surgery with 100% accuracy in all three patients. All SLNs were histologically and immunohistochemically negative. Patients had good cosmetic and functional results, and maintained their visual acuity and ocular motility.Conclusion: Patients with conjunctival melanoma can undergo preoperative lymphoscintigraphy and SLN biopsy safely using radioactive technetium and isosulfan blue dye. Keywords: ocular melanoma, sentinel lymph node biopsy, lymphoscintigraphy, conjunctival melanom