Publications of the Astronomical Society of the Pacific 89:704-705, October 1977 PHOTOMETRY OF THE FU ORIONIS STARS V1057 CYGNI AND V1515 CYGNF ARLO U. LANDOLTf Louisiana State University Observatory Received 1977 June 3 UBVR photoelectric data have been obtained for V1057 Cyg in 1975, 1976, and 1977. Its rate of fading has slowed to 0^0005 per day. Another FU Ori type object, V1515 Cyg, is found to have photoelectric colors essentially the same as V1057 Cyg. Key words: FU Orionis stars—variable stars—photometry—pre-main-sequence The FU Orionis class of variable star contains three Standard reduction procedures were followed. The rms identified members: V1057 Cygni, V1515 Cygni, and error of an individual observation is less than ±0.02 FU Ori itself. Existing observations indicate that these magnitude for both magnitude and color indices. objects were faint irregularly variable Τ Tauri-like stars The magnitude and color indices for V1057 Cyg before their outburst. The outbursts caused these stars have been tabulated in Table 1. A slow decrease in to rapidly brighten some 5 to 6 magnitudes. After the brightness is still discernable. When the photoelectric outburst, the stars roughly maintained their newly at- data of Table I are compared to those photoelectric tained brightness. Discussions of the nature of these data given by Landolt (1975), the Β magnitude shows a outbursts and characteristics of the stars themselves have been given by Herbig (1966, 1977), Grasdalen (1973), and Welin (19766z). Table I I. V1057 Cygni UBVR Photometry of V1057 Cygni The pre-main-sequence star V1057 Cyg (a = 20h55m19s, δ = +43°52:2; Δα = +2^15, Δδ = JD,Θ B-V U-B V-R 4-0^231 (1900)) underwent an outburst in 1969 (Welin 1971). A thorough discussion of the evolution of this 2442000.0+ object has been given by Grasdalen (1973). A photo- 761.57525 10.37 +1.50 + 1.14 electric sequence of stars in the neighborhood of 761.57725 10.35 1.58 0.99 V1057 Cyg was established by Landolt (1975). He 754.55170 10.47 1.58 1.07 764.57850 10.45 1.55 showed that the long-term decline in brightness was 1.02 755.57483 10.47 1.58 1.00 then proceeding at a rate of ^0^001 per day. Recent photographic results by Welin (1975, 1976¾) indicate 755.57574 10.47 1.58 0.94 that V1057 Cyg's decline in brightness may have end- 755.57878 10.52 1.58 1.07 ed. 765.58148 10.52 1.55 1.10 UBV photoelectric observations were made of V1057 1108.6137 10.64 1.61 1.09 + 1. 32 1108.5148 10.64 1.50 1.10 1. 36 Cyg at the Kitt Peak National Observatory (KPNO) no. 4 0.4-m telescope on eight nights in 1975, 1976, and 1109.5241 10.64 1.59 1.08 1.33 1977. UBVR data were obtained at the 2.1-m telescope 1109.6252 10.65 1.59 1.08 1.36 on three nights in 1976. The 0.4-m telescope data were 1111.5832 10.67 1.60 1.11 1.33 tied into Johnson (1963) standard stars. The 2.1-m data 1111.5841 10.57 1.50 1.12 1.33 were related to Landolt (1973) standards. The R meas- 1115.58813 10.70 1.55 1.10 ures were related to the Johnson UBVRI photometric 1115.59076 10.68 1.57 1.09 system, using standards supplied by Kunkel (1976). 1116.58512 10.70 1.58 1.15 1115.58794 10.59 1.58 1.13 1262.96580 10.58 1.61 1.09 * Contribution of Louisiana State University Observatory No. 126. 1262.98333 10.68 1.75: fVisiting Astronomer, 1975-77, at Kitt Peak National Observatory, which is operated by the Association of Universities for Research in 1263.96209 10.67 1.59 1.14 Astronomy, Inc., under contract with the National Science Founda- 1253.98552 10.58 1.88: tion. 704 © Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System PHOTOMETRY OF V1057 CYGNI AND V1515 CYGNI 705 rate of decline of 0^00056 per day. During the same Table II interval, JD2442216-2443112, the (B — V) color index has reddened by ^ 0^14. On the other hand, the UBVR Photometiy of V1515 Cygni (U — B) color index has reddened by less than 0^05, if at all. Four observations of V1057 Cyg were made in April JU V B-V U-B V-R 1977. The average Β magnitude has dropped another Ό 0^01; the color indices are virtually unchanged from early December 1976. The (B — V) indices marked by colons are uncertain due to rapidly approaching dawn. 2443000.0+ 106.6291 12.03 +1.57 +1.10 +1.30 IL V1515 Cygni 106.6305 12.02 1.58 1.04 1.30 A third FU Ori-like object was discovered by Herbig 107.6022 11.99 1.56 1.10 1.25 (Wenzel and Gessner 1975). Finding charts have been 107.6036 11.98 1.56 1.05 1.28 given by Wenzel and Gessner and by Cohen (1974). 107.6050 11.99 1.56 1.04 1.26 This object began increasing in brightness from ^ 16th 108.6070 11.96 1.58 1.10 1.24 magitude in the interval 1958-60 to its present bright- 108.6084 11.96 1.58 1.12 1.22 ness, Β ~ 13¾. The photometric history of this star 108.6101 11.96 1.58 1.12 1.26 has been tabulated by Herbig (1977). Cohen (1974) 109.6187 11.97 1.57 1.06 1.28 found no large signal at either 2μ or 10μ. 109.6200 11.97 1.54 1.09 1.27 Photoelectric observations were made at the KPNO 2.1-m telescope for V1515 Cyg in the same manner as 111.5794 12.01 1.58 1.05 1.29 described above for V1057 Cyg. The results are tabu- 111.5803 12.03 1.53 1.09 1.22 lated in Table II. A range of ^ 0^07 is evident over a five-night interval in both the magnitude and the color indices. This variation probably is real, for the accu- are currently changing little if any photometrically. racy of an individual observation is better than ^0^02 Continued photometric and spectroscopic monitoring, for a 12th magnitude object at the 2.1-m telescope. as pointed out by Herbig (1977), will be useful. Comparison of the present photometry with that of R. Stone (Herbig 1977) shows virtually no change ei- The author acknowledges with thanks the telescope ther in the magnitude or color indices, especially con- time at KPNO and the aid of the night assistants at the sidering that the star appears to fluctuate photo- 2.1-m telesope. This work was supported in part by the metrically to some extent. National Science Foundation (NSF) grant no. MPS 75- 01890 and by the Air Force Office of Scientific Re- III. Discussion search (AFOSR) grant no. 77-3218. The spectra of the three known FU Ori stars are REFERENCES similar: F or G supergiant-like (Herbig 1977). Recent Cohen, M. 1974, Pub. A.S.P. 86, 813. UBVRI photometry by Lee (1970) for FU Ori shows V Grasdalen, G. L. 1973, Ap. /. 182, 781. = 8.96, (B-V) = +1™38, (U-B) = +0^92, and Herbig, G. Η. 1966, Vistas in Astronomy 8, 109. (V—R) — +1^18. The present photometry indicates 1977, Ap. J. (in press). (V-R) = +1^26 for V1515 Cyg and (V-R) = Johnson, H. L. 1963, in Basic Astronomical Data, K. Aa. Strand, ed. + 1^34 for V1057 Cyg. The (V—R) color index values (Chicago: University of Chicago Press), p. 204. 1966, Ann. Rev. of Astr. and Ap. 4, 193. indicate a possible correlation with age, i.e., time since Kunkel, W. 1976 (private communication). outburst. Comparison of the observed (B — V), (V—R), Landolt, A. U. 1973, A.J. 78, 959. color indices for these three stars with the intrinsic col- 1975, Pub. A.S.P. 87, 379. or indices for giants and supergiants (Johnson 1966) Lee, T. A. 1970, Pub. A.S.P. 82, 765. shows the colors to much more nearly match those of Welin, G. 1971, Astr. and Ap. 12, 312. 1975, I.A.U. Inf. Bull. Var. Stars No. 1057. giants, in contradiction to information obtained from 1976a, Asir, and Ap. 49, 145. the spectra. 1976b, I.A.U. Inf. Bui. Var. Stars No. 1195. UBV photometry shows that all three FU Ori stars Wenzel, W., and Gessner, H. 1975, Mitt. Ver. Sterne 7 (no. 2), 23. © Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System .