Other
Scientific paper
Mar 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aas...186.3508a&link_type=abstract
American Astronomical Society, 186th AAS Meeting, #35.08; Bulletin of the American Astronomical Society, Vol. 27, p.860
Other
Scientific paper
The yellow giant 31 Comae (HD111812: G0 III) lies near the North Galatic Pole (b(II) = +89{fdg }6; l(II) = 114{fdg }9). Although 80 pc distant in the Coma Berenices open cluster, 31 Com is a strong EUV source. Recent HST/GHRS spectra of the star show surprisingly weak Mg II lambda2800 and H I lambda1215 interstellar absorptions. The neutral hydrogen column in that direction must be quite low, reminiscent of the interstellar ``void'' toward epsilon CMa discovered by the EUVE. Indeed, previous EUVE observations have shown that the lines of sight to the hot white dwarfs HZ 43 (b(II) = +84deg ; l(II) = 54deg ) and GD 153 (b(II) = +85deg ; l(II) = 317deg ) have very low columns, NH < 1*E(18) cm(-2) , suggesting another ``tunnel'' near the NGP. We modeled the GHRS spectra of 31 Com to determine whether there is a further northward extension of the HZ 43/GD 153 void. [-3mm] The interstellar Mg II h and k absorptions in the 31 Com spectrum are quite sharp, suggesting only a single velocity component along the line of sight (compared with several distinct clouds in the direction of epsilon CMa). Our preliminary modeling of the Mg II, H I, and D I ISM features indicates that xi_t , T, and [D/H] are similar to the values measured previously for the lines of sight toward the nearby stars Capella and Procyon. Furthermore, the bulk velocity (-2 km s(-1) , heliocentric) is the same as predicted for the local cloud. The inferred neutral hydrogen column, NH ~ 8*E(17) cm(-2) , is one of the smallest ever measured directly from the Lyalpha absorption. We speculate that the majority of the neutral gas in the direction of 31 Com lies very close to the Sun in a few pc extension of the local ``fluff'', and that the remainder of the sightline is quite rarified and probably hot. In all likelihood the HZ 43/GD 153 void is considerably larger than suspected previously. [-2mm] This work was supported by NASA grants GO-5323.01-93A (HST), S-56460-D (HST), and NAG5-2274 (EUVE).
Ayres Thomas R.
Diplas Athanassios
Linsky Jeffrey L.
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