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from VSSC97

New BAA comparison sequences for IP Peg

Bill Worraker

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.

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

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