VARIABLE-STARS IN THE NORTHEAST ARM INNER HALO REGION OF THE SMALL MAGELLANIC CLOUD

This paper reports results of a photographic investigation of variable stars in a 1 X 1.3 degree region near the Northeast Arm of the Small Magellanic Cloud (SMC). We have discovered 133 new variable stars in this field, and have determined periods and B lightcurves for 78 new and 72 previously known variables. Most of the variables identified in this field are faint (B > 16) Cepheids and RR Lyrae stars. At periods shorter than three days, the Cepheid period-luminosity relation splits into two sequences. The brighter sequence is occupied by Cepheids with lightcurves similar to those of RR Lyrae stars of Bailey type c. These stars are believed to be pulsating in the first overtone mode. The fainter sequence is occupied by Cepheids with lightcurves similar to those of RR Lyraes of Bailey type ab. These stars are believed to be pulsating in the fundamental mode. The fundamental mode Cepheids obey the relations [B] = 18.29-2.71 log P and, more tentatively, [M(B)] = -0.87-2.71 log P. The P-L relations for the first overtone and fundamental mode Cepheids appear to be related to, but are not identical with, those observed for anomalous Cepheids in the dwarf spheroidal systems. The peak in the period-frequency distribution for Cepheids in this field occurs near a period of 1.8 days. Relatively more short period Cepheids were identified in this survey than in the survey of SMC variables by Payne-Gaposchkin and Gaposchkin. The surface density of RR Lyrae variables in this field is comparable to that in the SMC field near NGC 121. This implies that RR Lyrae stars are not strongly concentrated either to the SMC bar or to the center of the SMC system. The period-amplitude relation for 22 RR Lyrae stars in this field resembles that found by Graham for RR Lyraes in the more outlying NGC 121 field.