Chandra Observations of Associates of η Carinae. I. Luminosities

The region around the η Carinae Nebula has three OB associations, which contain a Wolf-Rayet star and several massive O3 stars. An early Chandra ACIS-I image was centered on η Car and includes Trumpler 16 and part of Trumpler 14. The Chandra image confirms the well-known result that O and very early B stars are X-ray sources with LX ≃ 10-7Lbol over an X-ray luminosity range of about 100. Two new, anomalously strong X-ray sources have been found among the hot star population: Tr 16-244, a heavily reddened O3 I star, and Tr 16-22, a heavily reddened O8.5 V star. Two stars have an unusually large LX/Lbol: HD 93162, a Wolf-Rayet star (and possible binary), and Tr 16-22, a possible colliding-wind binary. In addition, a population of sources associated with cool stars is detected. In the color-magnitude diagram, these X-ray sources sit above the sequence of field stars in the Carina arm. The OB stars are on average more X-ray-luminous than the cool star X-ray sources. X-ray sources among A stars have X-ray luminosities similar to those of cooler stars and may be due to cooler companions. Upper limits are presented for B stars that are not detected in X-rays. These upper limits are also the upper limits for any cool companions that the hot stars may have. Hardness ratios are presented for the most luminous sources in bands 0.5-0.9, 0.9-1.5, and 1.5-2.04 keV. The available information on the binary nature of the hot stars is discussed, but binarity does not correlate with X-ray strength in a simple way.