Harold Corwin

IC 1995 is one of the "exterior nebulosities of the Pleiades" found in the 1890s by Barnard on photographs generally taken at Lick Observatory. He has a long discussion of these, with drawings and a photograph, in MNRAS 60, 258, 1900. Most of these are either reflection nebulae associated with the Pleiades, or are dust clouds above the plane of the Galaxy reflecting its light back to us.

Though Barnard puts the center of his nebula at 03 44, +25.4 (for 1900), he goes on to say that "This is at the 6m star Piazzi iii. 170, which is Rad. 434, and whose position for 1860 is 03 43 54.30, +25 09 15.3." For 1900, this is 03 44 18.0, +25 16 46, a little south of the central position.

On the POSS plates, the nebula actually appears brightest south of the star (which is HD 23985 = SAO 76256), so I have chosen to take the position of the star as that for the nebula as well. Given the size of the nebula (at least a degree east-west and about half of that north-south), this is an acceptable position.

The actual position of the star is perhaps a bit uncertain. In this era of precision astrometry, I know this statement is verging on heretical. But the various catalogues have the star at slightly different positiions and with slightly different proper motions and parallaxes. I've put some into the main table.

I noticed two things in particular. First, Gaia EDR3 has no parallax or proper motions listed, apparently because -- second -- this is a double star, WDS 03503+2535. The Washington catalogue credits the discovery to Otto Struve in 1846 (though I'd have to check Struve's catalogues to be sure of the date). Hipparcos has the following information for the pair:

Comp     RA  (J2000)   Dec        pmRA  e_pm   pmDec  e_pm   Plx  e_px  V_T
  A  03 50 18.938  +25 34 45.66  +30.23 3.12  -130.88 1.68  16.96 0.82  5.73
  B  03 50 18.939  +25 34 45.79  +49.10 7.31   -91.17 3.80  16.96 0.82  6.52

All of this is to say that my preferred J2000.0 position -- from Hipparcos -- has some extra "cooking" in it. Caveat emptor!

― IC Notes by Harold Corwin

Drawings, descriptions, and CCD photos are copyright Andrew Cooper unless otherwise noted, no usage without permission.

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