Non-confirmation of reported clouds without optical counterparts in the Hercules cluster

¹ Observatoire de Paris, Section de Meudon, GEPI, CNRS UMR 8111, 5 place Jules Janssen, 92195 Meudon, France e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it. ;This email address is being protected from spambots. You need JavaScript enabled to view it. ;This email address is being protected from spambots. You need JavaScript enabled to view it.
² Arecibo Observatory, HC3 Box 53995, Arecibo, Puerto Rico 00612, USA e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it. ;This email address is being protected from spambots. You need JavaScript enabled to view it.
³ CNRS URA 2052 and CEA, DSM, DAPNIA, Service d'Astrophysique, Centre d'Études de Saclay, 91911 Gif-sur-Yvette Cedex, France e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
⁴ Department of Astronomy, University of Minnesota, Minneapolis, USA e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
⁵ Laboratoire d'Astrophysique de Marseille, Traverse du Siphon – Les Trois Lucs, 13376 Marseille, France e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
⁶ Universitäts-Sternwarte, Geismarlandstrasse 11, 37083 Göttingen, Germany e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
⁷ Instituto de Astrofísica de Andalucía (CSIC), Granada, Spain e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
⁸ Astronomy Department, University of Virginia, Charlottesville, VA 22903, USA e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Corresponding author: W. van Driel, This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 30 August 2002
Accepted: 7 November 2002

Abstract

21 cm H i line observations were made with the Arecibo Gregorian telescope of 9 H i clouds in the Hercules Cluster which were reported as tentative detections in a VLA H i study of the cluster (Dickey [CITE]) and for which our deep CCD imaging failed to find any optical counterparts. No sensitive observations could be made of one of these (sw-174) due to the presence of a close-by strong continuum source. The other 8 tentative H i detections were not confirmed by the Arecibo H i measurements. The CCD images did reveal faint, low surface brightness counterparts near the centres of two other VLA H i sources invisible on the Palomar Sky Survey, sw-103 and sw-194.