25 research outputs found
Retrieval of Precise Radial Velocities from Near-Infrared High Resolution Spectra of Low Mass Stars
Given that low-mass stars have intrinsically low luminosities at optical
wavelengths and a propensity for stellar activity, it is advantageous for
radial velocity (RV) surveys of these objects to use near-infrared (NIR)
wavelengths. In this work we describe and test a novel RV extraction pipeline
dedicated to retrieving RVs from low mass stars using NIR spectra taken by the
CSHELL spectrograph at the NASA Infrared Telescope Facility, where a methane
isotopologue gas cell is used for wavelength calibration. The pipeline
minimizes the residuals between the observations and a spectral model composed
of templates for the target star, the gas cell, and atmospheric telluric
absorption; models of the line spread function, continuum curvature, and
sinusoidal fringing; and a parameterization of the wavelength solution. The
stellar template is derived iteratively from the science observations
themselves without a need for separate observations dedicated to retrieving it.
Despite limitations from CSHELL's narrow wavelength range and instrumental
systematics, we are able to (1) obtain an RV precision of 35 m/s for the RV
standard star GJ 15 A over a time baseline of 817 days, reaching the photon
noise limit for our attained SNR, (2) achieve ~3 m/s RV precision for the M
giant SV Peg over a baseline of several days and confirm its long-term RV trend
due to stellar pulsations, as well as obtain nightly noise floors of ~2 - 6
m/s, and (3) show that our data are consistent with the known masses, periods,
and orbital eccentricities of the two most massive planets orbiting GJ 876.
Future applications of our pipeline to RV surveys using the next generation of
NIR spectrographs, such as iSHELL, will enable the potential detection of
Super-Earths and Mini-Neptunes in the habitable zones of M dwarfs.Comment: 64 pages, 28 figures, 5 tables. Accepted for publication in PAS
First radial velocity results from the MINiature Exoplanet Radial Velocity Array (MINERVA)
The MINiature Exoplanet Radial Velocity Array (MINERVA) is a dedicated
observatory of four 0.7m robotic telescopes fiber-fed to a KiwiSpec
spectrograph. The MINERVA mission is to discover super-Earths in the habitable
zones of nearby stars. This can be accomplished with MINERVA's unique
combination of high precision and high cadence over long time periods. In this
work, we detail changes to the MINERVA facility that have occurred since our
previous paper. We then describe MINERVA's robotic control software, the
process by which we perform 1D spectral extraction, and our forward modeling
Doppler pipeline. In the process of improving our forward modeling procedure,
we found that our spectrograph's intrinsic instrumental profile is stable for
at least nine months. Because of that, we characterized our instrumental
profile with a time-independent, cubic spline function based on the profile in
the cross dispersion direction, with which we achieved a radial velocity
precision similar to using a conventional "sum-of-Gaussians" instrumental
profile: 1.8 m s over 1.5 months on the RV standard star HD 122064.
Therefore, we conclude that the instrumental profile need not be perfectly
accurate as long as it is stable. In addition, we observed 51 Peg and our
results are consistent with the literature, confirming our spectrograph and
Doppler pipeline are producing accurate and precise radial velocities.Comment: 22 pages, 9 figures, submitted to PASP, Peer-Reviewed and Accepte
Validating AU Microscopii d with Transit Timing Variations
AU Mic is a young (22 Myr) nearby exoplanetary system that exhibits excess
TTVs that cannot be accounted for by the two known transiting planets nor
stellar activity. We present the statistical "validation" of the tentative
planet AU Mic d (even though there are examples of "confirmed" planets with
ambiguous orbital periods). We add 18 new transits and nine midpoint times in
an updated TTV analysis to prior work. We perform the joint modeling of transit
light curves using EXOFASTv2 and extract the transit midpoint times. Next, we
construct an O-C diagram and use Exo-Striker to model the TTVs. We generate TTV
log-likelihood periodograms to explore possible solutions for the period of
planet d and then follow those up with detailed TTV and RV MCMC modeling and
stability tests. We find several candidate periods for AU Mic d, all of which
are near resonances with AU Mic b and c of varying order. Based on our model
comparisons, the most-favored orbital period of AU Mic d is 12.73596+/-0.00793
days (T_{C,d}=2458340.55781+/-0.11641 BJD), which puts the three planets near a
4:6:9 mean-motion orbital resonance. The mass for d is 1.053+/-0.511 M_E,
making this planet Earth-like in mass. If confirmed, AU Mic d would be the
first known Earth-mass planet orbiting a young star and would provide a
valuable opportunity in probing a young terrestrial planet's atmosphere.
Additional TTV observation of the AU Mic system are needed to further constrain
the planetary masses, search for possible transits of AU Mic d, and detect
possible additional planets beyond AU Mic c.Comment: 89 pages, 35 figures, 34 tables. Redid EXOFASTv2 transit modeling to
recover more reasonable stellar posteriors, so redid Exo-Striker TTV modeling
for consistency. Despite these changes, the overall results remain unchanged:
the 12-7-day case is still the most favored. Submitted to AAS Journals on
2023 Feb 9t
Validating AU Microscopii d with Transit Timing Variations
AU Mic is a young (22 Myr), nearby exoplanetary system that exhibits excess transit timing variations (TTVs) that cannot be accounted for by the two known transiting planets nor stellar activity. We present the statistical âvalidationâ of the tentative planet AU Mic d (even though there are examples of âconfirmedâ planets with ambiguous orbital periods). We add 18 new transits and nine midpoint times in an updated TTV analysis to prior work. We perform the joint modeling of transit light curves using EXOFASTv2 and extract the transit midpoint times. Next, we construct an O â C diagram and use Exo-Striker to model the TTVs. We generate TTV log-likelihood periodograms to explore possible solutions for dâs period, then follow those up with detailed TTV and radial velocity Markov Chain Monte Carlo modeling and stability tests. We find several candidate periods for AU Mic d, all of which are near resonances with AU Mic b and c of varying order. Based on our model comparisons, the most-favored orbital period of AU Mic d is 12.73596 ± 0.00793 days ( T _C _,d = 2458340.55781 ± 0.11641 BJD), which puts the three planets near 4:6:9 mean-motion resonance. The mass for d is 1.053 ± 0.511 M _â , making this planet Earth-like in mass. If confirmed, AU Mic d would be the first known Earth-mass planet orbiting a young star and would provide a valuable opportunity in probing a young terrestrial planetâs atmosphere. Additional TTV observations of the AU Mic system are needed to further constrain the planetary masses, search for possible transits of AU Mic d, and detect possible additional planets beyond AU Mic c