Photometric and Spectroscopic Observations of a Filamentary IR-Emitting Diffuse Interstellar Cloud near the LMC
Session 12 -- Interstellar medium
Display presentation, Monday, 9, 1995, 9:20am - 6:30pm

## [12.01] Photometric and Spectroscopic Observations of a Filamentary IR-Emitting Diffuse Interstellar Cloud near the LMC

B. Penprase, J. Lauer, J. Aufrecht (Pomona College, Claremont, CA 91711)

We report the results of a photometric and spectroscopic study of stars which appear toward an infrared bright filament near the LMC. The filament was chosen for study due to its large angular size, intense IR emission, and proximity to an X-ray source observed by Wang using the ROSAT satellite. We have observed 38 stars in the vicinity of the filament with combined $uvby$-H$\beta$ photometry, and two stars with a high resolution spectrograph ($\lambda/\delta\lambda$ $>$ 70,000) in the wavelength of the Ca II K line. From our observations of the stars toward the filament, we have derived a distance estimate of 130 $\pm$ 40 pc for the cloud, and a mean color excess E(B-V) = 0.17 $\pm$ 0.05 magnitudes. The resulting extinction toward the cloud is A$_{v}$=0.53 magnitudes, assuming R$_{v}$ = 3.1. We have also observed strikingly different Ca II absorption line profiles in the spectra of two of the stars. The sightline toward HD 22252 has at least seven separate components of Ca II absorption, while the sightline toward HD 26109 appears to have only a single component. The spectroscopic results suggest that the warm gas component of the filament traced by Ca II has very different kinematics from one end to the other, perhaps as a result of shock excitation. Examination of IRAS colors for the cloud suggests a similar contrast in the dust environment from one end of the cloud to the other, with values of R(12,100), and R(60,100) enhanced by more than a factor of two at the high galactic latitude end of the cloud near the HD 22252 sightline. By combining our distance estimate with the ROSAT X-ray intensity we may derive an estimate of the density of the hot component of the ISM in the local bubble of n$_{e}$ = 4.5 x 10$^{-3}$ cm$^{-3}$. The cloud is in fairly close proximity to the $\beta$ CMa tunnel, (l, b= 230, -15), and it may be possible that the Geminga supernova (l, b=290, -43) may have ejected this filament. The IR filament appears to offer an excellent laboratory for probing a wide range of interstellar conditions within a single diffuse interstellar cloud.