The nearby star α Oph (Ras Alhague) is a rapidly rotating A5IV star spinning at ∼ 89% of its breakup velocity. Indeed, we calculate that the presence of this M-dwarf companion easily accounts for the X-ray emission from this star detected by ROSAT. A system such as this may provide insight into the anomalous X-ray emission from A stars, hypothesized to be from unseen late-type stellar companions. Moreover, the frequency of binary companions can help to discriminate between binary formation scenarios that predict an abundance of low-mass companions forming from the early fragmentation of a massive circumstellar disk. Multiplicity studies of higher mass stars are relatively rare, and binary companions such as this one at the extreme low end of the mass ratio distribution are useful additions to surveys incomplete at such a low mass ratio. We see clear evidence for orbital motion from this companion and are able to constrain the semimajor axis to be ∼>24.9 AU, the period ∼>124 yr, and eccentricity ∼>0.16. Assuming the two objects are coeval, this mass suggests an M4V-M7V spectral type for the companion, which is confirmed through integral field spectroscopic measurements. Using evolutionary models, we estimate its mass to be 0.168 +0.012 -0.016 M sun, giving a mass ratio for this system q = 0.082 +0.007 -0.008. This companion is ∼7 mag fainter than its host star in the H band, and infrared imaging spanning 4.75 years over five epochs indicates this companion has common proper motion with its host star. Through the combination of high-order adaptive optics and coronagraphy, we report the discovery of a faint stellar companion to the A3V star ζ Virginis. The discovery of a low-mass (∼0.25 M sun) companion around a bright (V = 4.0 mag), nearby (d= 25 pc) star highlights a region of binary star parameter space that to date has not been fully probed. This common parallax method is potentially more rigorous than common proper motion, ensuring that the neighboring bodies lie at the same distance, rather than relying on the statistical improbability that two objects in close proximity to each other on the sky move in the same direction. Our measurements demonstrate common parallactic and proper motion over the course of 103 days, significantly shorter than the period of time needed for most companion confirmations through proper motion measurements alone. The use of an astrometric pupil plane grid allowed us to determine the projected separations between the companion and the coronagraphically occulted primary star to ≤3 mas precision at two observation epochs. Imaging spectroscopy combined with adaptive optics coronagraphy allowed for the detection and spectrophotometric characterization of the point source at a contrast of ∼6 J- and H-band magnitudes and separation of 1'' from the primary star. The A5V star Alcor has an M3-M4 dwarf companion, as evidenced by a novel astrometric technique. In addition to the astronomical results, the analysis presented helps validate the Project 1640 data reduction and spectral extraction processes and the utility of low-resolution, near-infrared spectra for characterizing late-type companions in multiple systems. Together, these data increase our knowledge and understanding of the stellar make up of these systems. We also present several new epochs of astrometry of each of the systems. Additionally, we determine effective temperature and surface gravity of the companions by fitting synthetic spectra calculated with the PHOENIX model atmosphere code. With this comparison, we test the accuracy and consistency of spectral-type determination with the low-resolution near-infrared spectra from P1640. The reduced, extracted, and calibrated spectra were compared to template spectra from the IRTF spectral library. Five of these stars are known binary stars and we detected the late-type secondaries and were able to measure their JH spectra with a resolution of R ∼ 30. We used the Project 1640 near-infrared coronagraph and integral field spectrograph to observe 19 young solar-type stars.
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