12 research outputs found
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
A high-precision near-infrared survey for radial velocity variable low-mass stars using CSHELL and a methane gas cell
We present the results of a precise near-infrared (NIR) radial velocity (RV) survey of 32 low-mass stars with spectral types K2-M4 using CSHELL at the NASA InfraRed Telescope Facility in the K band with an isotopologue methane gas cell to achieve wavelength calibration and a novel, iterative RV extraction method. We surveyed 14 members of young (â25-150 Myr) moving groups, the young field star Ï” Eridani, and 18 nearby (<25 pc) low-mass stars and achieved typical single-measurement precisions of 8-15 m s-1with a long-term stability of 15-50 m s-1 over longer baselines. We obtain the best NIR RV constraints to date on 27 targets in our sample, 19 of which were never followed by high-precision RV surveys. Our results indicate that very active stars can display long-term RV variations as low as âŒ25-50 m s-1 at â2.3125 ÎŒm, thus constraining the effect of jitter at these wavelengths. We provide the first multiwavelength confirmation of GJ 876 bc and independently retrieve orbital parameters consistent with previous studies. We recovered RV variabilities for HD 160934 AB and GJ 725 AB that are consistent with their known binary orbits, and nine other targets are candidate RV variables with a statistical significance of 3Ï-5Ï. Our method, combined with the new iSHELL spectrograph, will yield long-term RV precisions of âČ5 m s-1 in the NIR, which will allow the detection of super-Earths near the habitable zone of mid-M dwarfs
Transit Timing Variations for AU Microscopii b & c
We explore the transit timing variations (TTVs) of the young (22 Myr) nearby
AU Mic planetary system. For AU Mic b, we introduce three Spitzer (4.5 m)
transits, five TESS transits, 11 LCO transits, one PEST transit, one Brierfield
transit, and two transit timing measurements from Rossiter-McLaughlin
observations; for AU Mic c, we introduce three TESS transits. We present two
independent TTV analyses. First, we use EXOFASTv2 to jointly model the Spitzer
and ground-based transits and to obtain the midpoint transit times. We then
construct an O--C diagram and model the TTVs with Exo-Striker. Second, we
reproduce our results with an independent photodynamical analysis. We recover a
TTV mass for AU Mic c of 10.8 M. We compare the
TTV-derived constraints to a recent radial-velocity (RV) mass determination. We
also observe excess TTVs that do not appear to be consistent with the dynamical
interactions of b and c alone, and do not appear to be due to spots or flares.
Thus, we present a hypothetical non-transiting "middle-d" candidate exoplanet
that is consistent with the observed TTVs, the candidate RV signal, and would
establish the AU Mic system as a compact resonant multi-planet chain in a 4:6:9
period commensurability. These results demonstrate that the AU Mic planetary
system is dynamically interacting producing detectable TTVs, and the implied
orbital dynamics may inform the formation mechanisms for this young system. We
recommend future RV and TTV observations of AU Mic b and c to further constrain
the masses and to confirm the existence of possible additional planet(s).Comment: Corrected typos; revised Section 3, 4, and 5 to reflect reanalysis,
results unchanged. Submitted to AAS Journals Nov 11th, 2020; favorable
referee report received Jan 3rd; final draft accepted for publication in the
AJ Apr 19t
Transit timing variations for AU Microscopii b and c
P.P.P. acknowledges support from NASA (Exoplanet Research Program award No. 80NSSC20K0251, TESS Cycle 3 Guest Investigator Program award No. 80NSSC21K0349, JPL Research and Technology Development, and Keck Observatory Data Analysis), the NSF (Astronomy and Astrophysics grant Nos. 1716202 and 2006517), and the Mt. Cuba Astronomical Foundation. D.D. acknowledges support from the TESS Guest Investigator Program grant No. 80NSSC21K0108 and NASA Exoplanet Research Program grant No. 18-2XRP18_2-0136. E.G. acknowledges support from NASA Exoplanet Research Program award No. 80NSSC20K0251. The material is based upon work supported by NASA under award No. 80GSFC21M0002. L.D.V. acknowledges funding support from the Heising-Simons Astrophysics Postdoctoral Launch Program through a grant to Vanderbilt University.We explore the transit timing variations (TTVs) of the young (22 Myr) nearby AU Mic planetary system. For AU Mic b, we introduce three Spitzer (4.5 ÎŒm) transits, five TESS transits, 11 LCO transits, one PEST transit, one Brierfield transit, and two transit timing measurements from RossiterâMcLaughlin observations; for AU Mic c, we introduce three TESS transits. We present two independent TTV analyses. First, we use EXOFASTv2 to jointly model the Spitzer and ground-based transits and obtain the midpoint transit times. We then construct an O â C diagram and model the TTVs with Exo-Striker. Second, we reproduce our results with an independent photodynamical analysis. We recover a TTV mass for AU Mic c of 10.8â2.2+2.3 Mâ. We compare the TTV-derived constraints to a recent radial velocity (RV) mass determination. We also observe excess TTVs that do not appear to be consistent with the dynamical interactions of b and c alone or due to spots or flares. Thus, we present a hypothetical nontransiting âmiddle-dâ candidate exoplanet that is consistent with the observed TTVs and candidate RV signal and would establish the AU Mic system as a compact resonant multiplanet chain in a 4:6:9 period commensurability. These results demonstrate that the AU Mic planetary system is dynamically interacting, producing detectable TTVs, and the implied orbital dynamics may inform the formation mechanisms for this young system. We recommend future RV and TTV observations of AU Mic b and c to further constrain the masses and confirm the existence of possible additional planet(s).Publisher PDFPeer reviewe
Transit Timing Variations for AU Microscopii b & c
We explore the transit timing variations (TTVs) of the young (22 Myr) nearby
AU Mic planetary system. For AU Mic b, we introduce three Spitzer (4.5 m)
transits, five TESS transits, 11 LCO transits, one PEST transit, one Brierfield
transit, and two transit timing measurements from Rossiter-McLaughlin
observations; for aumic c, we introduce three ess Cycle transits. We present
two independent TTV analyses. First, we use EXOFASTv2 to jointly model the
Spitzer and ground-based transits and to obtain the midpoint transit times. We
then construct an O-C diagram and model the TTVs with Exo-Striker. Second, we
reproduce our results with an independent photodynamical analysis. We recover a
TTV mass for AU Mic c of 10.8 M. We compare the
TTV-derived constraints to a recent radial-velocity (RV) mass determination. We
also observe excess TTVs that do not appear to be consistent with the dynamical
interactions of b and c alone, and do not appear to be due to spots or flares.
Thus, we present a hypothetical non-transiting "middle-d" candidate exoplanet
that is consistent with the observed TTVs, the candidate RV signal, and would
establish the AU Mic system as a compact resonant multi-planet chain in a 4:6:9
period commensurability. These results demonstrate that the AU Mic planetary
system is dynamically interacting producing detectable TTVs, and the implied
orbital dynamics may inform the formation mechanisms for this young system. We
recommend future RV and TTV observations of AU Mic b and c to further constrain
the masses and to confirm the existence of possible additional planet(s)
Diving Beneath the Sea of Stellar Activity: Chromatic Radial Velocities of the Young AU Mic Planetary System
We present updated radial-velocity (RV) analyses of the AU Mic system. AU Mic is a young (22 Myr) early-M dwarf known to host two transiting planets - P b ⌠8.46 days, Rb=4.38-0.18+0.18 R oplus, P c ⌠18.86 days, R c=3.51-0.16+0.16 R oplus. With visible RVs from Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical echelle Spectrographs (CARMENES)-VIS, CHIRON, HARPS, HIRES, Minerva-Australis, and Tillinghast Reflector Echelle Spectrograph, as well as near-infrared (NIR) RVs from CARMENES-NIR, CSHELL, IRD, iSHELL, NIRSPEC, and SPIRou, we provide a 5Ï upper limit to the mass of AU Mic c of M c †20.13 M â and present a refined mass of AU Mic b of M b=20.12-1.57+1.72 M oplus. Used in our analyses is a new RV modeling toolkit to exploit the wavelength dependence of stellar activity present in our RVs via wavelength-dependent Gaussian processes. By obtaining near-simultaneous visible and near-infrared RVs, we also compute the temporal evolution of RV 'color' and introduce a regressional method to aid in isolating Keplerian from stellar activity signals when modeling RVs in future works. Using a multiwavelength Gaussian process model, we demonstrate the ability to recover injected planets at 5Ï significance with semi-amplitudes down to â10 m s-1 with a known ephemeris, more than an order of magnitude below the stellar activity amplitude. However, we find that the accuracy of the recovered semi-amplitudes is âŒ50% for such signals with our model