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The infrared void in the Lupus dark clouds revisited: a polarimetric approach
The results of B-band CCD imaging linear polarimetry obtained for starsfrom the Hipparcos catalogue are used to re-examine the distribution ofthe local interstellar medium towards the IRAS 100-μm emission voidin the Lupus dark clouds. The analysis of the obtainedparallax-polarization diagram assigns to the dark cloud Lupus1 adistance between 130 and 150pc and assures the existence of a low columndensity region coincident with the observed infrared void. Moreover,there are clear indications of the existence of absorbing material atdistances closer than 60-100pc, which may be associated with theinterface boundary between the Local Bubble and its neighbourhood LoopIsuperbubble.
| The Spectra of T Dwarfs. II. Red Optical Data
We present 6300-10100 Å spectra for a sample of 13 T dwarfsobserved using LRIS mountedtpdel 99 on the Keck I 10 m Telescope. Avariety of features are identified and analyzed, includingpressure-broadened K I and Na I doublets; narrow Cs I and Rb I lines;weak CaH, CrH, and FeH bands; strong H2O absorption; and apossible weak CH4 band. Hα emission is detected inthree of the T dwarfs, strong in the previously reported active T dwarf2MASS 1237+6526 and weak in SDSS 1254-0122 and 2MASS 1047+2124. None ofthe T dwarfs exhibit Li I absorption. Guided by the evolution of opticalspectral features with near-infrared spectral type, we derive a paralleloptical classification scheme, focusing on spectral types T5 to T8,anchored to select spectral standards. We find general agreement betweenoptical and near-infrared types for nearly all the T dwarfs so farobserved, including two earlier type T dwarfs, within our classificationuncertainties (~1 subtype). These results suggest that competing gravityand temperature effects compensate for each other over the 0.6-2.5 μmspectral region. We identify one possible means of disentangling theseeffects by comparing the strength of the K I red wing to the 9250Å H2O band. One of our objects, 2MASS 0937+2931,exhibits a peculiar spectrum with a substantial red slope and relativelystrong FeH absorption, both consequences of a metal-deficientatmosphere. On the basis of its near-infrared properties and substantialspace motion, this object may be a thick disk or halo brown dwarf.
| On the infrared void in the Lupus dark clouds
Strömgren uvbyβ photometry observations obtained for 205 starsin the general direction of a void in the IRAS 100-μm emission fromthe Lupus dark cloud complex are presented and analysed. The colourexcess versus distance diagram confirms the existence of a regiondepleted from interstellar material, which is also seen in the ROSATsoft X-ray background emission map. The distance to the surroundingmaterial is estimated as being within the interval from 60 to 100pc.This result is in disagreement with previous distance estimates to thesupposed supernova that has been suggested as responsible for clearingthe region from dust. As an alternative, the data presented support thesuggestion that the void may have been produced by the detachment ofmaterial from the interface between LoopI and the Local Bubble as aconsequence of hydromagnetic instabilities. Moreover, the distributionof colour excess as a function of distance supports a value of ~150pc asthe most probable distance to the dark cloud known as Lupus1.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
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Observation and Astrometry data
| Constellation: | Вага |
| Right ascension: | 15h35m52.46s |
| Declination: | -29°34'24.8" |
| Apparent magnitude: | 9.011 |
| Distance: | 154.083 parsecs |
| Proper motion RA: | -12.5 |
| Proper motion Dec: | -0.9 |
| B-T magnitude: | 9.667 |
| V-T magnitude: | 9.066 |
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