Publications of the Astronomical Society of the Pacific 97:165-174, Febmary 1985 PHOTOMETRY OF STARS IN THE uvgr SYSTEM* STEPHEN M. KENT Harvard-Smithsonian Center for Astrophysics, 60 Garden Street Cambridge, Massachusetts 02138 Received 1984 July 23, revised 1984 November 17 Photoelectric photometry is presented for over 400 stars using the uvgr system of Thuan and Gunn. Stars were selected to cover a wide range of spectral type, luminosity class, and metallicity. A mean main sequence is derived along with red- dening curves and approximate transformations to the UBVR system. The calibration of the standard-star sequence is sig- nificantly improved. Key words: photometry—stellar classification I. Introduction II. Observations The uvgr system (Thuan and Gunn 1976, hereafter The observations were made during several runs from TG) was developed as a four-color intermediate-to-wide- 1976 through 1978 on the Palomar 60-inch (1.5-m) tele- band photometric system which was designed to avoid a scope. The instrumentation and equipment were identi- number of pitfalls of the standard UBV system. The four cal with that used by TG. A two-channel pulse-counting bands are nonoverlapping and exclude the strongest S20 photometer allowed for the simultaneous measure- night-sky lines. The u and ν filters lie in a region of ment of object and sky. Each star was observed in both strong line blanketing in late-type stars and measure the apertures except for the globular-cluster stars, where it Balmer jump in early-type stars; the g and r filters lie in was necessary to go off the cluster to measure sky. This less-affected regions and hence provide a measure of redundancy was useful in eliminating errant observations stellar temperature. All filters have closed bandpasses (as might be caused by a star in the sky hole). An aper- and hence the system is not sensitive to the wavelength ture size of 15" was used at all times. Integration times cutoff of the particular detector being used. The uvgr were typically 5 or 10 seconds on bright stars and pro- system has become somewhat popular for use with new portionately longer on faint ones. Each channel and each imaging devices such as CCDs where the darkness and night was reduced independently. Errors on bright ob- well-defined bandpasses of the g and r filters are espe- jects (g < 12) are estimated to be < 0^02 rms. On the cially appreciated. Results in the uvgr system published faint globular-cluster stars, errors are estimated to be thus far include studies of globular clusters by Zinn somewhat larger, perhaps 0^05 in the u filter and 0^03 (1980) and Searle, Wilkinson, and Bagnuolo (1980), first- in the others. Crowded fields also contribute to this ranked galaxies in clusters by Hoessel, Gunn, and Thuan error. (1980), and surface photometry of M31 by Hoessel and During one night of observations it was discovered Melnick (1980). part way through the night that the infamous 60-inch In this paper, the photometry of over 400 field and dome (which operates under computer control) was par- cluster stars is reported. An attempt has been made to tially occulting the telescope. Normally one would take observe stars with a wide diversity of types in order to the data from such a night and deposit it in the nearest establish the ability of the system to distinguish stars of trash can. However, it was found subsequently upon re- different classes. Types observed include main-sequence ducing the standard-star observations that, while the stars, giants and supergiants, subdwarfs, white dwarfs, magnitudes were indeed rubbish, the color indices gave globular-cluster stars, galactic-cluster stars, and a few quite reasonable solutions. Hence the reduced color in- other miscellaneous stars. A mean main sequence is de- dices from this night have been retained, and such ob- fined and reddening curves are derived. The ability of jects are marked in the tables by having a blank in the the system to separate stars of different luminosities and magnitude column. metallicities is demonstrated. Finally, improved magni- Stars were selected from a wide variety of sources tudes and color indices are given for most of the funda- which are described in the succeeding sections. In gener- mental standard stars. al, all objects have UBV observations available as well. III. Standard Stars "Research reported here was begun while the author was at Palo- Early on it became evident that the accuracy of the mar Observatory, California Institute of Technology. standard stars originally measured by TG could be im- 165 © Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System 166 STEPHEN M. KENT proved. A recalibration of the standards was therefore directly as it did originally. Nevertheless its new magni- undertaken. In the first step, twelve stars in the fall sky tude and color indices differ from the old by at most which were observed simultaneously on four nights were 0^01. reduced by standard techniques using the original mag- For reference, the mean extinction coefficients de- nitudes and color indices given by TG. Using the residu- rived from the standard solutions are listed in Table II. als derived from the least-squares solutions, a mean cor- IV. System Characteristics rection was applied to each star. After applying these corrections, the rms residuals in the least-squares solu- In advance of presenting the new photometry, some of tions were reduced to 0^07 per observation. This new the characteristics of the uvgr system are first discussed. set of magnitudes and color indices defined a new pri- A. Main Sequence mary set of standards. Additional standard-star observa- A mean main sequence will be plotted in all figures. It tions were then reduced directly to this fundamental set. was derived using stars with good spectral types in the The revised set of standard stars is listed in Table I. Pleiades, Hyades, and M 34 (with small reddening cor- Not all original standard stars were reobserved suffi- rections applied where necessary) and selected field ciently, and for these the original TG values are re- stars. The main sequence so derived is listed in Table III. tained. One star, Wilson 12754, has been dropped, as it Values for spectral types earlier than AO are somewhat was in a very crowded field. Another, Ross 451, has also uncertain because unreddened stars of these types are been dropped since it became clear that the published too bright to observe with a 60-inch telescope. No values color indices are in error, but not enough new observa- are listed for M dwarfs because not very many stars of tions were made to derive better values. Two new stars these types were observed and the colors of these stars (GL745A and B) have been added; both are quite red are a quite sensitive function of spectral type. subdwarfs. The coordinates for Ross 786 in TG were giv- en for epoch 1950 by mistake; the correct 1900 coordi- nates are given here. TABLE II With this new calibration, +17 4708 no longer de- fines the zero-point of the magnitudes and color indices Atmospheric Extinction Coefficients Term Coefficient TABLE I -0.179 Standard Stars v-g -0.171 Object o(1900) 6(1900) v-g g-r -0.212 h 0 BD +71 31 00 37?l +71 38 10.21 -0.04 0.01 -0.03 -0.093 HD 19445 03 02.5 +25 59 8.088 -0.008 -0.087 0.018 *g-r Ross 374 03 21.1 +23 26 10.851 0.096 0.000 0.079 Ross 34 03 22.3 +37 03 11.523 1.257 0.397 0.937 BD +21 607 04 08.6 +22 06 9.241 -0.011 -0.036 -0.016 BD +54 1216 08 11.7 +54 25 9.727 0.019 -0.053 0.002 TABLE III BD +25 1981 08 38.5 +25 10 9.277 -0.089 0.102 -0.159 Ross 683 08 45.1 +08 00 11.40 0.46 -0.01 0.25 Ross 889 09 35.6 +01 29 10.45 -0.08 0.01 -0.08 Standard Main Sequence HD 84937 09 43.5 +14 14 8.34 -0.06 0.01 -0.06 Felge 34 10 33.8 +43 37 10.893 -0.825 -0.755 -0.787 Spectral Class V-g U—V g—r BD +29 2091 10 41.8 +28 57 10.330 0.068 -0.106 0.080 Ross 453 12 05.8 +00 58 11.119 -0.007 -0.062 0.015 Feige 67 12 39.2 +17 49 11.534 -0.829 -0.749 -0.792 ^ -0.84 -0.77 -0.80 Ross 484 13 13.8 -02 32 11.092 0.915 0.231 0.571 B5 -0.61 -0.30 -0.68 BD +26 2606 14 44.6 +26 08 9.759 -0.019 -0.032 0.006 AO -0.37 0.36 -0.56 BD +2 3375 17 34.8 +02 28 9.987 0.002 -0.042 0.040 A5 -0.17 0.42 -0.40 HD 171164 18 28.1 +28 48 8.376 1.080 0.501 0.518 **0 -0.02 0.24 -0.19 Ross 711 18 31.4 +28 38 11.437 -0.039 -0.039 0.010 GL 745A 19 02.8 +20 44 11.359 1.438 0.477 1.205 Ρ5 0.12 0.09 -0.02 GL 745B 19 02.8 +20 44 11.348 1.434 0.480 1.202 0,05 BD +35 3659 19 27.6 +35 57 10.281 0.060 -0.067 0.050 G5 0.42 0.09 0.14 BD +28 4211 21 46.7 +28 24 10.214 -0.837 -0.767 -0.800 K0 0.66 0.18 0.28 BD +17 4708 22 06.7 +17 36 9.500 0.001 -0.001 0.001 ire 1 Π* Π 47 η HD 215732 22 42.2 +29 22 8.157 1.302 0.618 0.649 ' ' 'D Ross 786 23 04.5 +00 12 10.059 0.356 -0.045 0.242 K8 1.29 0.46 0.79 © Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System uvgr PHOTOMETRY OF STARS 167 B.