Prior Indigenous Technological Species

One of the primary open questions of astrobiology is whether there is extant or extinct life elsewhere the Solar System. Implicit in much of this work is that we are looking for microbial or, at best, unintelligent life, even though technological artifacts might be much easier to find. SETI work on searches for alien artifacts in the Solar System typically presumes that such artifacts would be of extrasolar origin, even though life is known to have existed in the Solar System, on Earth, for eons. But if a prior technological, perhaps spacefaring, species ever arose in the Solar System, it might have produced artifacts or other technosignatures that have survived to present day, meaning Solar System artifact SETI provides a potential path to resolving astrobiology's question. Here, I discuss the origins and possible locations for technosignatures of such a $prior$ $indigenous$ $technological$ $species$, which might have arisen on ancient Earth or another body, such as a pre-greenhouse Venus or a wet Mars. In the case of Venus, the arrival of its global greenhouse and potential resurfacing might have erased all evidence of its existence on the Venusian surface. In the case of Earth, erosion and, ultimately, plate tectonics may have erased most such evidence if the species lived Gyr ago. Remaining indigenous technosignatures might be expected to be extremely old, limiting the places they might still be found to beneath the surfaces of Mars and the Moon, or in the outer Solar System.Comment: 11pp, no figures. Accepted for publication in the International Journal of Astrobiology. v2: Added some important reference

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 $\beta$. 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.Comment: 2 pages v2. reflects revisions from editorial process v3. includes doi and journal referenc

Twenty Years of Precise Radial Velocities at Keck and Lick Observatories

The precise radial velocity survey at Keck Observatory began over 20 years ago. Its survey of thousands of stars now has the time baseline to be sensitive to planets with decade-long orbits, including Jupiter analogs. I present several newly-finished orbital solutions for long-period giant planets. Although hot Jupiters are generally "lonely" (i.e. they are not part of multiplanet systems), those that are not appear to often have giant companions at 5 AU or beyond. I present two of the highest period- ratios among planets in a two-planet system, and some of the longest orbital periods ever measured for exoplanets. In many cases, combining Keck radial velocities from those from other long-term surveys at Lick Observatory, McDonald Observatory, HARPS, and, of course, OHP spectrographs, produces superior orbital fits, constraining both period and eccentricity better than could be possible with any single set alone. Stellar magnetic activity cycles can masquerade as long-period planets. In most cases this effect is very small, but a loud minority of stars, including, apparently, HD 154345, show very strong RV-activity correlations.Comment: 10 pages, 9 Figures and photos Video of talk here: http://interferometer.osupytheas.fr/colloques/OHP2015/videos/Jason_Wright.mp4 Conference program here: http://ohp2015.sciencesconf.org/resource/page/id/9, Edited by I. Boisse, O. Demangeon, F. Bouchy & L. Arnol

On Distinguishing Interstellar Objects Like `Oumuamua From Products of Solar System Scattering

Schneider (2018) explored the possibility that 'Oumuamua is a Solar System object, and concluded that if it is, it must have been scattered by "another, yet unknown planet." I provide an extremely conservative upper limit on post-scattering velocities in the Solar System to show that 'Oumuamua is moving far to quickly to be the result of any hypothetical single scattering event between any bound Solar System objects within 21 au (a distance within which our understanding of objects capable of scattering 'Oumuamua is presumably complete).Comment: This version has reference added not in origina

Proving Heliocentrism and Measuring the Astronomical Unit in a Laboratory Astronomy Class via the Aberration of Starlight

The objective reality of the Earth's motion about the Sun was finally proven observationally by Bradley (1727) when he correctly explained the ~20'' annual, elliptical motions of stars as being due to aberration of starlight caused by the motion of the Earth. This effect can be detected today with ordinary astrophotographic equipment by measuring the coordinates of the center of star trails, which reveal the apparent position of the Celestial Poles, which vary due to the aberration of starlight, in addition to the effects of the nutation and precession of Earth's Poles. Despite my aspirations, I have not found the time to even begin the project of measuring the aberration. I nonetheless feel that it is a rich project in observational astronomy and fundamental physics, and a pleasingly didactic exercise appropriate for upper-division undergraduate and graduate astronomy and physics laboratory classes, whose complexity and length may be justified by the novelty of proving heliocentrism with nothing but a small telescope and camera. I therefore publish this Research Note to disseminate the idea in hopes that I might receive word in a few years of a triumphant astronomy class's proof of heliocentrism, along with their best estimates of the astronomical unit and precession.Comment: http://adsabs.harvard.edu/abs/2018RNAAS...2c.119

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.Comment: 3 pp Research Note of the AAS. v.2 contains additional citation to prior art by Lingam & Loeb (2018) Astrobiology 18, 96

The putative old, nearby cluster Lod\'{e}n 1 does not exist

Astronomers have access to precious few nearby, middle-aged benchmark star clusters. Within 500 pc, there are only NGC 752 and Ruprecht 147 (R147), at 1.5 and 3 Gyr respectively. The Database for Galactic Open Clusters (WEBDA) also lists Lod\'{e}n 1 as a 2 Gyr cluster at a distance of 360 pc. If this is true, Lod\'{e}n 1 could become a useful benchmark cluster. This work details our investigation of Lod\'{e}n 1. We assembled archival astrometry (PPMXL) and photometry (2MASS, Tycho-2, APASS), and acquired medium resolution spectra for radial velocity measurements with the Robert Stobie Spectrograph (RSS) at the Southern African Large Telescope. We observed no sign of a cluster main-sequence turnoff or red giant branch amongst all stars in the field brighter than $J < 11$. Considering the 29 stars identified by L.O. Lod\'{e}n and listed on SIMBAD as the members of Lod\'{e}n 1, we found no compelling evidence of kinematic clustering in proper motion or radial velocity. Most of these candidates are A stars and red giants, and their observed properties are consistent with distant field stars in the direction of Lod\'{e}n 1 in the Galactic plane. We conclude that the old nearby cluster Lod\'{e}n 1 is neither old, nor nearby, nor a cluster.Comment: Accepted to A

The Third Workshop on Extremely Precise Radial Velocities: The New Instruments

The Third Workshop on Extremely Precise Radial Velocities was held at the Penn Stater Conference Center and Hotel in State College, Pennsylvania, USA from 2016 August 14 to 17, and featured over 120 registrants from around the world. Here we provide a brief description of the conference, its format, and its session topics and chairs. 23 instrument teams were represented in plenary talks, and we present a table containing the basic characteristics of their new precise Doppler velocimeters.Comment: Table available as PDF at https://psu.app.box.com/s/vyue4u5mnzswx1y2k3z0gnyct596da5

Exoplanet Detection Methods

This chapter reviews various methods of detecting planetary companions to stars from an observational perspective, focusing on radial velocities, astrometry, direct imaging, transits, and gravitational microlensing. For each method, this chapter first derives or summarizes the basic observable phenomena that are used to infer the ex- istence of planetary companions, as well as the physical properties of the planets and host stars that can be derived from the measurement of these signals. This chapter then outlines the general experimental requirements to robustly detect the signals us- ing each method, by comparing their magnitude to the typical sources of measurement uncertainty. This chapter goes on to compare the various methods to each other by outlining the regions of planet and host star parameter space where each method is most sensitive, stressing the complementarity of the ensemble of the methods at our disposal. Finally, there is a brief review of the history of the young exoplanet field, from the first detections to current state-of-the-art surveys for rocky worlds.Comment: 60 pp, 12 figures. To appear as Chapter 59 of "Planets, Stars, and Stellar Systems" Editor-in-chief Terry Oswalt, volume editor Paul Kalas. v.2 corrects typo, adds citatio

On Lloyd's "The Mass Distribution of Subgiant Planet Hosts" (arXiv:1306.6627v1)

We provide an informal response to James P. Lloyd's recent arXiv preprint (arXiv:1306.6627v1) "The Mass Distribution of Subgiant Planet Hosts", accepted for publication by Astrophysical Journal Letters.Comment: 3pp, 1 figure, arXiv-only postin