[vsnet-chat 2835] Sequence & position for V1830 Sgr

["Bruce Sumner" <b.sumner@bom.gov.au>]

151. V1830 SAGITTARII   (UG)   Range: 12.019?
     Position:   18 13 50.59  27 42 20.4  (J2000)
     Magnitude: 
                                                            
ID     RA  (2000)   DEC       X    Y  N    V      ERR     BV    ERR 

1   18 13 45.5  27 41 17   70   65  1  10.342  0.001   0.035  0.001   
2   18 14 06.3  27 38 31   207  230  2  10.938  0.004   0.629  0.021   
3   18 13 59.7  27 36 19   119  362  2  11.630  0.016   0.553  0.010   
4   18 13 36.7  27 37 55  186  266  3  12.227  0.019   0.561  0.009   
5   18 13 43.3  27 38 49   98  213  3  12.366  0.017   0.173  0.008   
5a  18 13 50.6  27 42 12    1    9  3  12.402  0.024   1.573  0.015   
6   18 13 57.2  27 41 34    86   47  3  12.656  0.016   0.520  0.013   
7   18 13 39.0  27 39 52  156  149  2  12.998  0.042   0.398  0.010   
8   18 13 52.3  27 41 41    21   40  2  13.385  0.012   1.589  0.005   
9   18 13 46.4  27 42 20   57    1  2  13.589  0.025   1.470  0.004   
10  18 13 54.8  27 42 07    54   14  2  13.929  0.017   0.602  0.008   
11  18 13 44.0  27 42 35   89  14  2  14.418  0.012   1.258  0.010   
12  18 13 48.6  27 43 03   28  42  2  14.886  0.006   1.643  0.003   
13  18 13 51.4  27 42 51     9  30  2  15.436  0.027   1.579  0.010   
14  18 13 50.5  27 42 29    2   8  2  15.809  0.031   1.608  0.025   
15  18 13 49.9  27 42 38   11  17  2  16.002  0.011   0.709  0.012   

Notes:

1. The close companion to V1830 Sgr, located only 8 arcsec to the north,
and here called 5a, is very red, and visually will appear to be about
magnitude 12.7, using the transformation v=V+0.2*(BV). It should not be
used as a comparison star, and is only included here because of earlier
questions about its magnitude. Vogt's magnitude of 12.03V (Publ. VSS, 
RASNZ, No 5, 1977) is clearly incorrect.

2. V1830 Sgr was caught in outburst on a DSS SERCV 4 minute exposure 
taken on 18 May 1987. It is located 0.38 arcsec east and 8.01 arcsec 
south of the 12.402V red star 5a discussed above. This gives V1830 Sgr 
the approximate coordinates, using UCAC1, of 18h 13m 50.59s 27d 42' 20.4" 
(J2000).

3. The sequence given here is far from ideal as it contains too many red
stars. There are basically two ranges of stars in this sequence, those 
with BV near 0.6 ('normal' colour), and those with BV near 1.6 (quite 
red). Stars in the second range, namely 8 and 9, and 11 to 14, will appear 
about 0.2 magnitude fainter visually than those comparison stars with 
more 'normal' colours.

4. Thanks to Arne Henden for obtaining the raw data for this sequence and 
for his perseverance in obtaining photometry in this very crowded field.

Bruce Sumner
19 April 2000

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