arXiv subjects

Jason T. Wright

Publications and source records attributed to Jason T. Wright.

At least 127 records · Page 7Linked to original sources

arXiv2019

The Effects of Telluric Contamination in Iodine Calibrated Precise Radial Velocities

We characterized the effects of telluric absorption lines on the radial velocity (RV) precision of stellar spectra taken through an iodine cell. To isolate the effects induced by telluric contamination from other stellar, instrumental, or numerical systematic RV noise, we extracted RVs from simulated iodine calibrated spectra of three RV standard stars regularly observed by Keck/HIRES. We add in water absorption lines according to measured precipitable water vapor (PWV) contents over a one-year period. We concluded that telluric contamination introduces additional RV noise and spurious periodic signals on the level of 10-20 cm/s, consistent with similar previous studies. Our findings show that forward modeling the telluric lines effectively recovers the RV precision and accuracy, with no prior knowledge of the PWV needed. Such a recovery is less effective when the water absorption lines are relatively deep in the stellar template used in the forward modeling. Overall, telluric contamination plays an insignificant role for typical iodine-calibrated RV programs aiming at ~1-2 m/s, but we recommend adding modeling of telluric lines and taking stellar template observations on nights with low humidity for programs aiming to achieve sub-m/s precision.

astro-ph.EP↗

arXiv2019

Minerva-Australis I: Design, Commissioning, & First Photometric Results

The Minerva-Australis telescope array is a facility dedicated to the follow-up, confirmation, characterisation, and mass measurement of bright transiting planets discovered by the Transiting Exoplanet Survey Satellite (TESS) -- a category in which it is almost unique in the southern hemisphere. It is located at the University of Southern Queensland's Mount Kent Observatory near Toowoomba, Australia. Its flexible design enables multiple 0.7m robotic telescopes to be used both in combination, and independently, for high-resolution spectroscopy and precision photometry of TESS transit planet candidates. Minerva-Australis also enables complementary studies of exoplanet spin-orbit alignments via Doppler observations of the Rossiter-McLaughlin effect, radial velocity searches for non-transiting planets, planet searches using transit timing variations, and ephemeris refinement for TESS planets. In this first paper, we describe the design, photometric instrumentation, software, and science goals of Minerva-Australis, and note key differences from its Northern hemisphere counterpart -- the Minerva array. We use recent transit observations of four planets--WASP-2b, WASP-44b, WASP-45b, and HD 189733b to demonstrate the photometric capabilities of Minerva-Australis.

astro-ph.IM↗

arXiv2019

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$^{-1}$ 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.

astro-ph.IM↗

arXiv2019

KELT-24b: A 5M$_{\rm J}$ Planet on a 5.6 day Well-Aligned Orbit around the Young V=8.3 F-star HD 93148

We present the discovery of KELT-24 b, a massive hot Jupiter orbiting a bright (V=8.3 mag, K=7.2 mag) young F-star with a period of 5.6 days. The host star, KELT-24 (HD 93148), has a $T_{\rm eff}$ =$6509^{+50}_{-49}$ K, a mass of $M_{*}$ = $1.460^{+0.055}_{-0.059}$ $M_{\odot}$, radius of $R_{*}$ = $1.506\pm0.022$ $R_{\odot}$, and an age of $0.78^{+0.61}_{-0.42}$ Gyr. Its planetary companion (KELT-24 b) has a radius of $R_{\rm P}$ = $1.272\pm0.021$ $R_{\rm J}$, a mass of $M_{\rm P}$ = $5.18^{+0.21}_{-0.22}$ $M_{\rm J}$, and from Doppler tomographic observations, we find that the planet's orbit is well-aligned to its host star's projected spin axis ($λ$ = $2.6^{+5.1}_{-3.6}$). The young age estimated for KELT-24 suggests that it only recently started to evolve from the zero-age main sequence. KELT-24 is the brightest star known to host a transiting giant planet with a period between 5 and 10 days. Although the circularization timescale is much longer than the age of the system, we do not detect a large eccentricity or significant misalignment that is expected from dynamical migration. The brightness of its host star and its moderate surface gravity make KELT-24b an intriguing target for detailed atmospheric characterization through spectroscopic emission measurements since it would bridge the current literature results that have primarily focused on lower mass hot Jupiters and a few brown dwarfs.

astro-ph.EP↗

arXiv2019

Photon-weighted barycentric correction and its importance for precise radial velocities

When applying the barycentric correction to a precise radial velocity measurement, it is common practice to calculate its value only at the photon-weighted midpoint time of the observation instead of integrating over the entire exposure. However, since the barycentric correction does not change linearly with time, this leads to systematic errors in the derived radial velocities. The typical magnitude of this second-order effect is of order 10 cm s$^{-1}$, but it depends on several parameters, e.g. the latitude of the observatory, the position of the target on the sky, and the exposure time. We show that there are realistic observing scenarios, where the errors can amount to more than 1 ms$^{-1}$. We therefore recommend that instruments operating in this regime always record and store the exposure meter flux curve (or a similar measure) to be used as photon-weights for the barycentric correction. In existing data, if the flux curve is no longer available, we argue that second-order errors in the barycentric correction can be mitigated by adding a correction term assuming constant flux.

astro-ph.EP↗

arXiv2019

Towards a Comprehensive Bibliography for SETI

In this work, we motivate, describe, and announce a living bibliography for academic papers and other works published in the Search for Extraterrestrial Intelligence (SETI). The bibliography makes use of bibliographic groups (bibgroups) in the NASA Astrophysics Data System (ADS), allowing it to be accessed and searched by any interested party, and is composed only of works which have a presence on the ADS. We establish criteria that describe the scope of our bibliography, which we define as any academic work which broadly: 1) advances knowledge within SETI, 2) deals with topics that are fundamentally related to or about SETI, or 3) is useful for the better understanding of SETI, and which has a presence on ADS. We discuss the future work needed to continue the development of the bibliography. The bibliography can be found by using the bibgroup field (bibgroup: SETI) in the ADS search engine.

cs.DL↗

arXiv2019

Technosignatures in the Thermal Infrared

WISE, Gaia, and JWST provide an opportunity to compute the first robust upper limits on the energy supplies of extraterrestrial civilizations, both for stars in the Galaxy (Kardashev Type II civilizations) and for other galaxies (Kardashev Type III civilizations). Together, they allow for a nearly-complete catalog of nearby stars with infrared excesses, which is valuable for both stellar astrophysics and searches for technosignatures; and of the MIR luminosities of galaxies, important for studies of galaxies' star and star-formation properties, but also for the identification of potential galaxies endemic with alien technology. JWST will provide the crucial mid-infrared spectroscopy necessary to identify the origin of these infrared excesses, advancing both traditional astronomy and searches for technosignatures. Such signatures are distinguished from dust by their lack of far-infrared emission and lack of association with star formation.

astro-ph.IM↗

arXiv2019

Technosignatures in Transit

Kepler, K2, TESS, and similar time-domain photometric projects, while designed with exoplanet detection in mind, are also well-suited projects for searches for large artificial structures orbiting other stars in the Galaxy. An effort to examine these data sets with an eye towards non-spherical or otherwise anomalous transit events, and a robust follow-up program to understand the stars and occulters that generate them, would enable the first robust upper limits on such megastructures in terms of their sizes, occurrence rates, and orbital properties. Such work also has the ancillary benefit of improving our understanding of stellar photometric variability and orbital and physical parameter estimation of exoplanets from photometric time series, and may lead to the identification of new, unexpected classes of stellar variables and exoplanets. Ultimately, searching for the most unusual and anomalous signatures benefits not only the search for technologies, but also the entire astronomical community by uncovering new mysteries to advance our understanding of the Universe.

astro-ph.IM↗

arXiv2019

Searches for Technosignatures in Astronomy and Astrophysics

The search for life beyond the Solar System-a major part of the Planetary Systems thematic area of the Astro2020 Decadal process-includes the search for technological life. Although financial support for such searches at the NSF and NASA and in past decadal surveys has been weak to nonexistent, recent advances in astrobiology, astrophysics, and advances in technical capability make searches for technosignatures a compelling theme for 2020-2030 and beyond.

astro-ph.IM↗

arXiv2019

Searches for Technosignatures: The State of the Profession

The search for life in the universe is a major theme of astronomy and astrophysics for the next decade. Searches for technosignatures are complementary to searches for biosignatures, in that they offer an alternative path to discovery, and address the question of whether complex (i.e. technological) life exists elsewhere in the Galaxy. This approach has been endorsed in prior Decadal Reviews and National Academies reports, and yet the field still receives almost no federal support in the US. Because of this lack of support, searches for technosignatures, precisely the part of the search of greatest public interest, suffers from a very small pool of trained practitioners. A major source of this issue is institutional inertia at NASA, which avoids the topic as a result of decades-past political grandstanding, conflation of the effort with non-scientific topics such as UFOs, and confusion regarding the scope of the term "SETI." The Astro2020 Decadal should address this issue by making developing the field an explicit priority for the next decade. It should recommend that NASA and the NSF support training and curricular development in the field in a way that supports equity and diversity, and make explicit calls for proposals to fund searches for technosignatures.

astro-ph.IM↗

arXiv2019

Advances in Precise Radial Velocimetry From Cross-Disciplinary Work in Heliophysics, Stellar Astronomy, and Instrumentation

Progress in stellar precise radial velocity work will require the stellar, exoplanetary, and instrument scientists in the precise RV community to be better engaged with the heliophysics community. This engagement will require funding for close collaboration among statisticians, heliophysicists, instrument builders, and stellar astronomers, dedicated meetings where the communities can learn about each other and interact inperson, and computational and observational resources to generate the appropriate synthetic and real data sets to drive and prove theoretical understanding of RV jitter.

astro-ph.SR↗

arXiv2019

TESS reveals that the nearby Pisces-Eridanus stellar stream is only 120 Myr old

Pisces-Eridanus (Psc-Eri), a nearby ($d$ $\simeq$ 80-226 pc) stellar stream stretching across $\approx$120 degrees of the sky, was recently discovered with Gaia data. The stream was claimed to be $\approx$1 Gyr old, which would make it an exceptional discovery for stellar astrophysics, as star clusters of that age are rare and tend to be distant, limiting their utility as benchmark samples. We test this old age for Psc-Eri in two ways. First, we compare the rotation periods for 101 low-mass members (measured using time series photometry from the Transiting Exoplanet Survey Satellite, TESS) to those of well-studied open clusters. Second, we identify 34 new high-mass candidate members, including the notable stars $λ$ Tauri (an Algol-type eclipsing binary) and HD 1160 (host to a directly imaged object near the hydrogen-burning limit). We conduct an isochronal analysis of the color--magnitude data for these highest-mass members, again comparing our results to those for open clusters. Both analyses show that the stream has an age consistent with that of the Pleiades, i.e., $\approx$120 Myr. This makes the Psc-Eri stream an exciting source of young benchmarkable stars and, potentially, exoplanets located in a more diffuse environment that is distinct from that of the Pleiades and of other dense star clusters.

astro-ph.SR↗

arXiv2019

Ultra-Stable Environment Control for the NEID Spectrometer: Design and Performance Demonstration

Two key areas of emphasis in contemporary experimental exoplanet science are the detailed characterization of transiting terrestrial planets, and the search for Earth analog planets to be targeted by future imaging missions. Both of these pursuits are dependent on an order-of-magnitude improvement in the measurement of stellar radial velocities (RV), setting a requirement on single-measurement instrumental uncertainty of order 10 cm/s. Achieving such extraordinary precision on a high-resolution spectrometer requires thermo-mechanically stabilizing the instrument to unprecedented levels. Here, we describe the Environment Control System (ECS) of the NEID Spectrometer, which will be commissioned on the 3.5 m WIYN Telescope at Kitt Peak National Observatory in 2019, and has a performance specification of on-sky RV precision < 50 cm/s. Because NEID's optical table and mounts are made from aluminum, which has a high coefficient of thermal expansion, sub-milliKelvin temperature control is especially critical. NEID inherits its ECS from that of the Habitable-zone Planet Finder (HPF), but with modifications for improved performance and operation near room temperature. Our full-system stability test shows the NEID system exceeds the already impressive performance of HPF, maintaining vacuum pressures below $10^{-6}$ Torr and an RMS temperature stability better than 0.4 mK over 30 days. Our ECS design is fully open-source; the design of our temperature-controlled vacuum chamber has already been made public, and here we release the electrical schematics for our custom Temperature Monitoring and Control (TMC) system.

astro-ph.IM↗

arXiv2019

Stellar Spectroscopy in the Near-infrared with a Laser Frequency Comb

The discovery and characterization of exoplanets around nearby stars is driven by profound scientific questions about the uniqueness of Earth and our Solar System, and the conditions under which life could exist elsewhere in our Galaxy. Doppler spectroscopy, or the radial velocity (RV) technique, has been used extensively to identify hundreds of exoplanets, but with notable challenges in detecting terrestrial mass planets orbiting within habitable zones. We describe infrared RV spectroscopy at the 10 m Hobby-Eberly telescope that leverages a 30 GHz electro-optic laser frequency comb with nanophotonic supercontinuum to calibrate the Habitable Zone Planet Finder spectrograph. Demonstrated instrument precision <10 cm/s and stellar RVs approaching 1 m/s open the path to discovery and confirmation of habitable zone planets around M-dwarfs, the most ubiquitous type of stars in our Galaxy.

astro-ph.EP↗

arXiv2019

The 1D Relativistic Doppler Formula is an Incorrect Approximation in Precise Radial Velocity Work

Stellar Doppler velocimetry determines a star's radial velocity $v_r$ via measurement of a redshift, $z$. At precisions below 10 m s$^{-1}$ conversion between the two quantities is complex, and care must be taken to properly account for the effects of relativity. One particular aspect of the problem that bears repeating is that the one-dimensional version of the relativistic Doppler formula, which does not distinguish between the motion of the source and the observer, is incorrect in this context, and indeed does not even provide the correct coefficient for variations in the second-order terms involving $β$. Nonetheless, it is often useful to report a redshift in the more familiar units of velocity without a rigorous calculation, and much code already exists that does this. In these cases it is important to clearly document which formula is being used, and I recommend simply (and explicitly) using the approximation $v_r \approx cz$. This choice is trivially inverted, does not misrepresent the degree of relativistic rigor that has been applied in translating between redshift and radial velocity, and is, I believe, the most commonly followed convention in astronomy and cosmology. I also briefly discuss the differences between the Wright & Eastman barycentric correction procedure and the Lindegren & Dravins barycentric radial velocity measure.

astro-ph.IM↗

arXiv2018

Retired A Stars and Their Companions VIII: 15 New Planetary Signals Around Subgiants and Transit Parameters for California Planet Search Planets with Subgiant Hosts

We present the discovery of 7 new planets and 8 planet candidates around subgiant stars, as additions to the known sample of planets around "retired A stars" (Johnson et al. 2006). Among these are the possible first 3-planet systems around subgiant stars, HD 163607 and HD 4917. Additionally, we present calculations of possible transit times, durations, depths, and probabilities for all known planets around subgiant (3 < log g < 4) stars, focused on possible transits during the TESS mission. While most have transit probabilities of 1-2%, we find that there are 3 planets with transit probabilities > 9%.

astro-ph.EP↗

arXiv2018

Planet-Planet Tides in the TRAPPIST-1 System

The star TRAPPIST-1 hosts a system of seven transiting, terrestrial exoplanets apparently in a resonant chain, at least some of which are in or near the Habitable Zone. Many have examined the roles of tides in this system, as tidal dissipation of the orbital energy of the planets may be relevant to both the rotational and orbital dynamics of the planets, as well as their habitability. Generally, tides are calculated as being due to the tides raised on the planets by the star, and tides raised on the star by the planets. I write this research note to point out a tidal effect that may be at least as important as the others in the TRAPPIST-1 system and which is so far unremarked upon in the literature: planet-planet tides. Under some reasonable assumptions, I find that for every planet $p$ in the TRAPPIST-1 system there exists some other planet $q$ for which the planet-planet dynamical tidal strain is within an order of magnitude of the stellar eccentricity tidal strain, and that the effects of planet $f$ on planet $g$ are in fact greater than that of the star on planet $g$. It is thus not obvious that planet-planet tides can be neglected in the TRAPPIST-1 exoplanetary system, especially the tides on planet $g$ due to planet $f$, if the planets are in synchronous rotation.

astro-ph.EP↗

arXiv2018

Recommendations from the Ad Hoc Committee on SETI Nomenclature

The Ad Hoc Committee on SETI Nomenclature was convened at the suggestion of Frank Drake after the Decoding Alien Intelligence Workshop at the SETI Institute in March 2018. The purpose of the committee was to recommend standardized definitions for terms, especially those that are used inconsistently in the literature and the scientific community. The committee sought to recommend definitions and terms that are a compromise among several desirable but occasionally inconsistent properties for such terms: 1) Consistency with the historical literature and common use in the field; 2) Consistency with the present literature and common use in the field; 3) Precision of meaning; 4) Consistency with the natural (i.e. everyday, non-jargon) meanings of terms; 5) Compatibility with non-English terms and definitions. The definitions in this report are restricted to technical, SETI contexts, where they may have jargon senses different from their everyday senses. In many cases we include terms only to deprecate them (in the sense of "to withdraw official support for or discourage the use of...in favor of a newer or better alternative", Merriam-Webster sense 4). This is a consensus document that the committee members all endorse; however, in many cases the individual members have (or have expressed in the past) more nuanced opinions on these terms that are not fully reflected here, for instance Almár (2008, Acta Astronautica, 68, 351), Denning (2008, NASA-SP-2009-4802 Ch. 3 pp.63-124), and Wright (2018, arXiv:1803.06972).

physics.pop-ph↗