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K-band Spectroscopy of AX J1841.0-0536 and IGR J19140+0951

ATel #983; Elisa Nespoli, Juan Fabregat (University of Valencia, Spain) and Ronald Mennickent (University of Concepcion, Chile)
on 30 Jan 2007; 10:35 UT
Credential Certification: Juan Fabregat (juan.fabregat@uv.es)

Subjects: Infra-Red, Binary, Neutron Star

Resubmission of ATel #982, in which the Authors and Title fields were changed by mistake. Sincere apologies.

Spectroscopy in the K band of the AX J1841.0-0536 and IGR J19140+0951 optical/infrared counterparts was obtained on 2006 July 14, using the SofI spectrograph/imager attached to the ESO 3.5m NTT in La Silla, Chile (ESO proposal 077.D-0578(A)). The spectra cover the 2.02-2.28 µm range with a dispersion of 4.62 Å/pixel and S/N~150. Observations were carried out in poor weather conditions, under a partially clouded sky.

AX J1841.0-0536 (IGR J18410-0535): We observed 2MASS 18410043-0535465, the optical/infrared counterpart identified by Halpern et al. (2004, ATel #289). The main lines in the spectrum are HeI (2.0581µm) in emission, and HeI (2.1126µm) and Br-gamma in absorption. In addition, NIII/CIII (2.1155µm) is present in emission, and CIV (2.069 and 2.078µm) in weak emission. These signatures are characteristic of a mid to late O type supergiant. However, the very weak or absent HeII (2.1885µm) line together with HeI (2.0581µm) seen in emission indicate a spectral type not earlier than O9-B0. The estimated spectral type is B0I, with an uncertainty of two subtypes. This classification confirms the nature of AX J1841.0-0536 as a Supergiant Fast X-ray Transient (SFXT), as proposed by several authors from its X-ray emission behavior (e.g. Negueruela et al. 2005, ESA-SP 604, 165).

IGR J19140+0951: We observed 2MASS J19140422+0952577, the infrared counterpart identified by in 't Zand et al. (2006, A&A 448, 1101). The spectrum is dominated by HeI (2.0581µm) in emission, and HeI (2.1126µm) and Br-gamma in absorption. NIII/CIII (2.1155µm) is also present as a weak emission line, while HeII (2.1885µm) is absent. The spectral type is estimated at B1I. IGR J19140+0951 is a Supergiant X-ray Binary (SGXB).