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Issue A&A
Volume 436, Number 3, June IV 2005
Page(s) L53 - L56
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:200500122



A&A 436, L53-L56 (2005)
DOI: 10.1051/0004-6361:200500122

Letter

Tiny H I clouds in the local ISM

R. Braun1 and N. Kanekar2

1  ASTRON, Postbox 2, 7990 AA Dwingeloo, The Netherlands
    e-mail: braun@astron.nl
2  National Radio Astronomy Observatory, Socorro, NM 87801, USA
    e-mail: nkanekar@aoc.nrao.edu

(Received 22 April 2005 / Accepted 9 May 2005)

Abstract
We report deep, high spectral resolution WSRT $\ion{H}{i}$ 21 cm observations of four high latitude compact radio sources, that have revealed a new population of tiny, discrete clouds in the diffuse ISM, with peak optical depths $\tau \sim 0.1 {-} 2$%, $\ion{H}{i}$ column densities of 0.4- $8 \times 10^{18}$ cm-2 and core temperatures of 20-80 K. Imaging detections confirm these low column densities and imply linear core dimensions of a few thousand AU, assuming a distance of 100 pc. The physical origin of these tiny $\ion{H}{i}$ structures and their distribution in the ISM is at present unknown. Further observations will be required to determine whether they are a ubiquitous component of the ISM.


Key words: ISM: clouds -- ISM: bubbles -- stars: winds, outflows -- Galaxy: solar neighbourhood

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