The plan to introduce a BAAVSS web page on IP Peg prompted requests for a new
comparison sequence based on reliable photometry.
High-quality professional V-band photometry on the IP Peg field has recently
been undertaken and published by Skiff1 and by Misselt2.
Both authors use the Landolt system of photometry, so resulting V-magnitudes
should be directly comparable. Stars B, C, 1, D of the old TA sequence
(listed as GMH940130) are covered by both, the maximum difference in V being
less than 0.03 mag (for star 1). Thus we have produced a new sequence of V
magnitudes based directly on the Skiff and Misselt results, Skiff's figures
being chosen for B,C, 1, and D since his statistical uncertainties are
generally smaller than Misselt's. These magnitudes should be suitable for
observers using CCDs with appropriate V-filtering.
Although it is common practice to use V-magnitudes directly for visual work (generally because no other useful photometric data is available), the colour response of the human eye, especially when fully dark-adapted, approximates to a combination of B and V. This problem has been investigated by Howarth and Bailey3, who recommend the formula mv = V + 0.16(B-V) as a good approximation to the average state of dark adaptation of the average human eye; their formula gives better results than pure V-magnitudes for visual work3,4, so we have used it to produce a new visual magnitude sequence for IP Peg based on instrumental photometry. The necessary values of B-V have been taken from Misselt2 where possible (stars B, C, 1,D, G and J), from Goranskij et al5 for star F, and estimated from b-y values from Skiff1 in other cases (stars A and E; b and y are the Stromgren blue and yellow filtered magnitudes respectively). Note that visual magnitudes appear fainter than V, which is a direct consequence of positive B-V values. B-V is positive for the large majority of stars in the Galaxy.
References
1. B.A. Skiff, 'Skiff on IP Peg', submission to VSNET dated 10th Oct 1994.
2. K.A. Misselt, PASP 108, pp.146-165, 1996.
3. I.D. Howarth & J. Bailey, JBAA 90, pp.265-272, 1980.
4. T. Brelstaff, C. Lloyd, T. Markham & D. McAdam, JBAA 107, pp.135-140, 1997.
5. V.P. Goranskij, S.Yu. Shugarov, E.I. Orlowsky & V.Yu. Rahimov, IBVS 2653, 1985.
Making important eclipse observations. New charts 186.03 A | B | C
