Characterizing Infrared Radial Velocity Jitter in Red Giant Stars
Abstract
Variation, or 'jitter,' in the measured radial velocities of a star may be due to external factors such as the presence of a companion and/or intrinsic ones such as the large-scale motion of the star's atmosphere. Though past literature studies show that jitter is larger for more evolved giants, this jitter is otherwise not well characterized in red giant stars. For example, it is unknown whether the jitter amplitude has a wavelength dependence, though studies may suggest it is smaller in the infrared. In this work, we aim to quantify and characterize the intrinsic radial velocity variation of hundreds of red giant stars, and investigate how the jitter varies with different stellar parameters. The public datasets of APOGEE/APOGEE-2 provide temperature, surface gravity, metallicity, and multi-epoch radial velocities of over 100,000 stars, and we quantify the stars' jitter behavior with statistics of the residual radial velocities (e.g., half peak-to-peak velocity, standard deviation, kurtosis.) Preliminary results suggest a positive relationship between temperature and both the half peak-to-peak velocities and the standard deviations. Previous literature shows that by considering whether the variation is periodic or random, we may begin to differentiate between intrinsic and extrinsic jitter. Random jitter is likely intrinsic, while periodic jitter could correspond to internal or external factors. The kurtosis of the residual radial velocities reveals whether our distribution is sinusoidal or gaussian. We expected to see kurtosis decrease as we progressed up the red giant branch, corresponding to an expected transition from random jitter to periodic. So far it has been absent, perhaps due to complication by highly eccentric systems. We will continue to investigate the relationships between stellar parameters and radial velocity jitter. Successfully characterizing and quantifying the jitter will provide a useful observational constraint on fundamental stellar physics and make it easier to detect low-mass or distant companions.
- Publication:
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American Astronomical Society Meeting Abstracts #235
- Pub Date:
- January 2020
- Bibcode:
- 2020AAS...23511020S