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J.V. Vallerga, N. Craig, H. Thai (Space Sciences Lab, U.C. Berkeley)
Unique to the all-sky survey of EUVE are the longer wavelength bandpasses of the "dagwood" (400 Å) and "tin" (600 Å) filters on the Scanner C instrument. Because of the high cross sections of H and He at these wavelengths, it was never expected that these bands would detect many sources, but the sources that were detected would become important because of their rarity.
One of the mysteries of the EUVE survey (Bowyer et al. ApJ Suppl. 102,129, 1996) are the large number of sources that were detected only in the two long wavelength bands. There are 35 sources that were detected in dagwood and/or tin and not in the two shorter wavelength bandpasses. Except for one source, none of the rest were identified with a candidate inside the EUVE error circle (3 arc min diameter) using the catalog searching techniques described in Bowyer et al. (1996).
We report on new EUVE observations of 8 sources from the EUVE all-sky survey: 2EUVE_J1533+337, 2EUVE_J1636-285, 2EUVE_J1244-596, EUVE_J1601-164, EUVE_J1703-018, EUVE_J1708-111, EUVE_J1712-248, EUVE_J2041-368. The observations were designed to increase the detection sensitivity by a factor of 10 by increasing the exposure and decreasing the effective PSF compared to the survey. Each source location was observed for approximateley 4 ksec in both the dagwood and tin photometric bandpasses. None were detected.
Given the count rates reported in the Second EUVE source catalog, all of these sources should have been detected with a S/N ratio greater than 10 and with a typical value of 50. These sources were classified in the "H" quality class of detection in the Second Catalog, which was the most stringent condition for claiming a detection with a calculated false detection rate of 2 objects for the whole catalog. Therefore, if real, these sources must be variable. We will report stringent upper limts to the flux from these sources as well as discussing possible candidate objects that are consistent with our results.
The author(s) of this abstract have provided an email address for comments about the abstract: jvv@ssl.berkeley.edu