NGC 1857

Number of stars per data source

	Reference  720 :    1 star
	Reference  731 :    1 star
	Reference  821 :   23 stars
	Reference 1142 :   15 stars

720: Guetter H.H.; (1980) Publ. Astron. Soc. Pacific 92, 215; UBV photoelectric photometry of 259 PZT stars; 1980PASP...92..215G
731: Guetter H.H., Hewitt A.V.; (1984) Publ. Astron. Soc. Pacific 96, 441; Photoelectric UBV photometry for 317 PZT and VZT stars; 1984PASP...96..441G
821: Purgathofer A.; (1964) Ann. Univ. Sternw. Wien 26 no 2; Dreifarben Photometrie in offenen Sternhaufen sowie in zwei Sternfelden in Cygnus
1142: Babu G.S.D; (1989) J. Astrophys. Astron. 10, 295; Study of young open clusters as tracers of spiral features in our Galaxy. Paper 4: Czernik 20 (OCL 427); 1989JApA...10..295B