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Life is homochiral and homochirality is a fundamental feature of living systems on Earth. While the exact mechanism that led to homochirality is still not fully understood, any realistic scenario on the origins of life needs to address the emergence of homochirality. In order to impose and maintain chirality in a prebiotic network, an environmental factor functioning as a chiral agent is demanded. Magnetized surfaces are prebiotically plausible chiral agents, shown to be effective in enantioseparation of ribose-aminooxazoline (RAO), a ribonucleic acid (RNA) precursor, due to the chiral-induced spin selectivity (CISS) effect. As such, mechanisms for breaking the magnetic symmetry of magnetic minerals are of the utmost importance. Here we report the avalanche magnetization of magnetite $(Fe_{3}O_{4})$ by the crystallization of enantiopure RAO. The observed breaking of the magnetic symmetry is induced by the chiral molecules due to the CISS effect and spreads out across the magnetic surface like an avalanche, providing a way to uniformly magnetize a magnetic surface without fully covering it. Considered together with our previous results on enantioseparation by crystallization on a magnetic surface, chirality-induced avalanche magnetization paves the way for a cooperative feedback between chiral molecules and magnetic surfaces. With this feedback, a weak natural bias in the net magnetization can be amplified and spin-selective processes can be accommodated on magnetic minerals on a persistent basis., 19 pages, 6 figures

Ultraviolet (UV) light plays a key role in surficial theories of the origin of life, and numerous studies have focused on constraining the atmospheric transmission of UV radiation on early Earth. However, the UV transmission of the natural waters in which origins-of-life chemistry (prebiotic chemistry) is postulated to have occurred is poorly constrained. In this work, we combine laboratory and literature-derived absorption spectra of potential aqueous-phase prebiotic UV absorbers with literature estimates of their concentrations on early Earth to constrain the prebiotic UV environment in marine and terrestrial natural waters, and consider the implications for prebiotic chemistry. We find that prebiotic freshwaters were largely transparent in the UV, contrary to assumptions by some models of prebiotic chemistry. Some waters, e.g., high-salinity waters like carbonate lakes, may be deficient in shortwave ($\leq220$ nm) UV flux. More dramatically, ferrous waters can be strongly UV-shielded, particularly if the Fe$^{2+}$ forms highly UV-absorbent species like Fe(CN)$_6^{4-}$. Such waters may be compelling venues for UV-averse origin-of-life scenarios, but are disfavorable for some UV-dependent prebiotic chemistries. UV light can trigger photochemistry even if attenuated through photochemical transformations of the absorber (e.g., $e^{-}_{aq}$ production from halide irradiation), which may have both constructive and destructive effects for prebiotic syntheses. Prebiotic chemistries invoking waters containing such absorbers must self-consistently account for the chemical effects of these transformations. The speciation and abundance of Fe$^{2+}$ in natural waters on early Earth is a major uncertainty, and should be prioritized for further investigation as it plays a major role in UV transmission in prebiotic natural waters., Accepted to Astrobiology. Associated measurements/code: https://github.com/sukritranjan/dirty-water-1/. Comments solicited

Carbon dioxide (CO2) is the major carbonaceous component of many planetary atmospheres including the Earth throughout its history, and prebiological chemistry that reduces this C1 feedstock to organics has accordingly been sought. Carbon fixation chemistry utilizing hydrogen as stoichiometric reductant tends to require high pressures and temperatures, and yields of products of potential use to nascent biology are low1 . Here we demonstrate efficient ultraviolet (UV) photoredox chemistry between CO2 and sulfite (SO3 2–) that generates organics and sulfate (SO4 2– ). The chemistry is initiated by electron photodetachment from SO3 2– giving sulfite radicals and hydrated electrons, which reduce CO2 to its radical anion. By subjecting individual products and putative intermediates to the reaction conditions and analyzing the resultant mixtures, a network of ensuing reactions that can rationalize the products was revealed. In this way it was further discovered that citrate, malate, succinate, and tartrate can be generated by irradiation of glycolate in the presence of SO3 2– . The simplicity of this carboxysulfitic chemistry and the widespread occurrence and abundance of its feedstocks suggest that it could have readily taken place on the early Earth as well as on the surfaces of many rocky planets. The environmental availability of the carboxylate products on Earth could have driven the development of central carbon metabolism before the advent of biological CO2 fixation.

Recent astronomical observations obtained with the Kepler and TESS missions and their related ground-based follow-ups revealed an abundance of exoplanets with a size intermediate between Earth and Neptune. A low occurrence rate of planets has been identified at around twice the size of Earth, known as the exoplanet radius gap or radius valley. We explore the geometry of this gap in the mass-radius diagram, with the help of a Mathematica plotting tool developed with the capability of manipulating exoplanet data in multidimensional parameter space, and with the help of visualized water equations of state in the temperature-density graph and the entropy-pressure graph. We show that the radius valley can be explained by a compositional difference between smaller, predominantly rocky planets and larger planets that exhibit greater compositional diversity including cosmic ices (water, ammonia, methane) and gaseous envelopes. In particular, among the larger planets, when viewed from the perspective of planet equilibrium temperature, the hot ones are consistent with ice-dominated composition without significant gaseous envelopes, while the cold ones have more diverse compositions, including various amounts of gaseous envelopes., Comment: 30 pages, 15 figures

We report the identification of 32 transiting-planet candidates in HATNet field G205. We describe the procedures that we have used to follow up these candidates with spectroscopic and photometric observations, and we present a status report on our interpretation of the 28 candidates for which we have follow-up observations. Eight are eclipsing binaries with orbital solutions whose periods are consistent with their photometric ephemerides; two of these spectroscopic orbits are singled-lined and six are double-lined. For one of the candidates, a nearby but fainter eclipsing binary proved to be the source for the HATNet light curve, due to blending in the HATNet images. Four of the candidates were found to be rotating more rapidly than v sin i = 50 kms −1 and were not pursued further. Thirteen of the candidates showed no significant velocity variation at the level of 0.5 to 1.0 kms −1 . Seven of these were eventually withdrawn as photometric false alarms based on an independent reanalysis using more sophisticated tools. Of the remaining six, one was put aside because a close visual companion proved to be a spectroscopic binary, and two were not followed up because the host stars were judged to be too large. Two of the remaining candidates are members of a visual binary, one of which was previously confirmed as the first HATNet transiting planet, HAT-P-1b. In this paper we confirm that the last of this set of candidates is also a a transiting planet, which we designate HAT-P-8b, with mass Mp = 1.52 +0.18 −0.16 MJ, radius Rp = 1.50 +0.08 −0.06 RJ, and photometric period P = 3.076320±0.000004 days. HAT-P-8b has an inflated radius for its mass, and a large mass for its period. The host star is a solar-metallicity F dwarf, with mass M⋆ = 1.28 ± 0.04 M⊙ and R⋆ = 1.58 +0.08 −0.06 R⊙. Subject headings: planetary systems — stars: individual (HAT-P-8, GSC 02757-01152) techniques: spectroscopic

The geometric Baade-Wesselink method is one of the most promising techniques for obtaining a better calibration of the Cepheid period-luminosity relation by means of interferometric measurements of accurate diameters. In this paper we present new wavelength- and phase-dependent limb darkening corrections based on our time-dependent hydrodynamic models of the classical Cepheid zeta Gem. We show that a model simulation of a Cepheid atmosphere, taking into account the hydrodynamic effects associated with the pulsation, shows strong departures from the limb darkening otherwise predicted by a static model. For most of its pulsational cycle the hydrodynamic model predicts a larger limb darkening then the equivalent static model. The hydrodynamics affects the limb darkening mainly at UV and optical wavelengths. Most of these effects evolve slowly as the star pulsates, but there are phases, associated with shocks propagating into the photosphere, in which significant changes in the limb darkening take place on time-scales of the order of less than a day. We assess the implication of our model LD corrections fitting the geometric Baade-Wesselink distance of zeta Gem for the available near-IR PTI data. We discuss the effects of our model limb darkening on the best fit result, and analyze the requirements needed to test the time-dependence of the limb darkening with future interferometric measurements., 22 pages, 5 figures, to be published on the Astrophysical Journal, June 1 2003 issue

The meeting started at 16h00. The president welcomed the 24 participants to the business meeting of Commission 27. After the approval of the agenda, she gave an overview of the activities of Commission 27 of the past three years.

We present Kepler observations of the bright (V=8.3), oscillating star HD 179070. The observations show transit-like events which reveal that the star is orbited every 2.8 days by a small, 1.6 R_Earth object. Seismic studies of HD 179070 using short cadence Kepler observations show that HD 179070 has a frequencypower spectrum consistent with solar-like oscillations that are acoustic p-modes. Asteroseismic analysis provides robust values for the mass and radius of HD 179070, 1.34{\pm}0.06 M{\circ} and 1.86{\pm}0.04 R{\circ} respectively, as well as yielding an age of 2.84{\pm}0.34 Gyr for this F5 subgiant. Together with ground-based follow-up observations, analysis of the Kepler light curves and image data, and blend scenario models, we conservatively show at the >99.7% confidence level (3{\sigma}) that the transit event is caused by a 1.64{\pm}0.04 R_Earth exoplanet in a 2.785755{\pm}0.000032 day orbit. The exoplanet is only 0.04 AU away from the star and our spectroscopic observations provide an upper limit to its mass of ~10 M_Earth (2-{\sigma}). HD 179070 is the brightest exoplanet host star yet discovered by Kepler., Comment: Accepted to ApJ

We report the distribution of planets as a function of planet radius (R_p), orbital period (P), and stellar effective temperature (Teff) for P < 50 day orbits around GK stars. These results are based on the 1,235 planets (formally "planet candidates") from the Kepler mission that include a nearly complete set of detected planets as small as 2 Earth radii (Re). For each of the 156,000 target stars we assess the detectability of planets as a function of R_p and P. We also correct for the geometric probability of transit, R*/a. We consider first stars within the "solar subset" having Teff = 4100-6100 K, logg = 4.0-4.9, and Kepler magnitude Kp < 15 mag. We include only those stars having noise low enough to permit detection of planets down to 2 Re. We count planets in small domains of R_p and P and divide by the included target stars to calculate planet occurrence in each domain. Occurrence of planets varies by more than three orders of magnitude and increases substantially down to the smallest radius (2 Re) and out to the longest orbital period (50 days, ~0.25 AU) in our study. For P < 50 days, the radius distribution is given by a power law, df/dlogR= k R^��. This rapid increase in planet occurrence with decreasing planet size agrees with core-accretion, but disagrees with population synthesis models. We fit occurrence as a function of P to a power law model with an exponential cutoff below a critical period P_0. For smaller planets, P_0 has larger values, suggesting that the "parking distance" for migrating planets moves outward with decreasing planet size. We also measured planet occurrence over Teff = 3600-7100 K, spanning M0 to F2 dwarfs. The occurrence of 2-4 Re planets in the Kepler field increases with decreasing Teff, making these small planets seven times more abundant around cool stars than the hottest stars in our sample. [abridged], Submitted to ApJ, 22 pages, 10 figures

This paper reports the discovery and characterization of the transiting hot giant exoplanet Kepler-17b. The planet has an orbital period of 1.486 days, and radial velocity measurements from the Hobby-Eberly Telescope show a Doppler signal of 419.5[superscript +13.3][subscript –15.6] m s[superscript –1]. From a transit-based estimate of the host star's mean density, combined with an estimate of the stellar effective temperature T[subscript eff] = 5630 ± 100 from high-resolution spectra, we infer a stellar host mass of 1.06 ± 0.07 M ⊙ and a stellar radius of 1.02 ± 0.03 R ⊙. We estimate the planet mass and radius to be M[subscript P] = 2.45 ± 0.11 M [subscript J] and R [subscript P] = 1.31 ± 0.02 R [subscript J]. The host star is active, with dark spots that are frequently occulted by the planet. The continuous monitoring of the star reveals a stellar rotation period of 11.89 days, eight times the planet's orbital period; this period ratio produces stroboscopic effects on the occulted starspots. The temporal pattern of these spot-crossing events shows that the planet's orbit is prograde and the star's obliquity is smaller than 15[degrees]. We detected planetary occultations of Kepler-17b with both the Kepler and Spitzer Space Telescopes. We use these observations to constrain the eccentricity, e, and find that it is consistent with a circular orbit (e < 0.011). The brightness temperatures of the planet's infrared bandpasses are T [subscript 3.6mum]=1880[plus or minus]100K and T[subscript 4.5mum]=1770 [plus or minus] 150K. We measure the optical geometric albedo A[subscript g] in the Kepler bandpass and find A[subscript g] = 0.10 ± 0.02. The observations are best described by atmospheric models for which most of the incident energy is re-radiated away from the day side., United States. National Aeronautics and Space Administration (NASA through an award issued by JPL/Caltech), W. M. Keck Foundation

Luminous low-mass stars of intermediate Teff – candidates for post-AGB transition objects to PNNi, are all expected to be pulsationally variable. Different modes and their combinations may be involved, leading to a variety of observed behaviour.

We report the discovery and the Rossiter-McLaughlin effect of Kepler-8b, a transiting planet identified by the NASA Kepler Mission. Kepler photometry and Keck-HIRES radial velocities yield the radius and mass of the planet around this F8IV subgiant host star. The planet has a radius RP = 1.419 RJ and a mass, MP = 0.60 MJ, yielding a density of 0.26 g cm^-3, among the lowest density planets known. The orbital period is P = 3.523 days and orbital semima jor axis is 0.0483+0.0006/-0.0012 AU. The star has a large rotational v sin i of 10.5 +/- 0.7 km s^-1 and is relatively faint (V = 13.89 mag), both properties deleterious to precise Doppler measurements. The velocities are indeed noisy, with scatter of 30 m s^-1, but exhibit a period and phase consistent with the planet implied by the photometry. We securely detect the Rossiter-McLaughlin effect, confirming the planet's existence and establishing its orbit as prograde. We measure an inclination between the projected planetary orbital axis and the projected stellar rotation axis of lambda = -26.9 +/- 4.6 deg, indicating a moderate inclination of the planetary orbit. Rossiter-McLaughlin measurements of a large sample of transiting planets from Kepler will provide a statistically robust measure of the true distribution of spin-orbit orientations for hot jupiters in general., 26 pages, 8 figures, 2 tables; In preparation for submission to the Astrophysical Journal

List of Figures. List of Tables. Preface. Contributing Authors. 1. A Historical Sketch of the Beat Cepheid Studies J.O. Petersen, M. Takeuti. 2. Double-Mode Stellar Pulsations Z. Kollath, J.R. Buchler. 3. The Multiperiodic Behavior of RR Lyrae Stars G. Kovacs. 4. RV Tauri Stars A.B. Fokin. 5. Pulsation and Mass Loss E.A. Dorfi, et al. 6. The model-oscillators of stellar pulsation Y. Tanaka. 7. Nonlinear Analysis of Irregular Variables J.R. Buchler, Z. Kollath. Index.

Light curves from the Kepler Mission contain valuable information on the nature of the phenomena producing the transit-like signals. To assist in exploring the possibility that they are due to an astrophysical false positive, we describe a procedure (BLENDER) to model the photometry in terms of a "blend" rather than a planet orbiting a star. A blend may consist of a background or foreground eclipsing binary (or star-planet pair) whose eclipses are attenuated by the light of the candidate and possibly other stars within the photometric aperture. We apply BLENDER to the case of Kepler-9, a target harboring two previously confirmed Saturn-size planets (Kepler-9b and Kepler-9c) showing transit timing variations, and an additional shallower signal with a 1.59-day period suggesting the presence of a super-Earth-size planet. Using BLENDER together with constraints from other follow-up observations we are able to rule out all blends for the two deeper signals, and provide independent validation of their planetary nature. For the shallower signal we rule out a large fraction of the false positives that might mimic the transits. The false alarm rate for remaining blends depends in part (and inversely) on the unknown frequency of small-size planets. Based on several realistic estimates of this frequency we conclude with very high confidence that this small signal is due to a super-Earth-size planet (Kepler-9d) in a multiple system, rather than a false positive. The radius is determined to be 1.64 (+0.19/-0.14) R(Earth), and current spectroscopic observations are as yet insufficient to establish its mass., Comment: 20 pages in emulateapj format, including 8 tables and 16 figures. To appear in ApJ, 1 January 2010. Accepted version

The problem of deriving the centre-of-mass velocity of a radially pulsating star is reexamined. New observations of line asymmetry and Non-LTE radiation hydrodynamics point to a systematic effect of about 1 km s−1 in Cepheids.

The first analysis of high-resolution IR spectra at 1.08 and 1.6 microns is presented for classical Cepheid variables. Three of the seven program stars were observed with complete phase coverage. The photospheric lines in the spectra were measured for asymmetries and compared to synthetic profiles from model atmospheres. An additional absorption component is shown to appear at certain phases in the 1.08 micron lines of X Sgr, Delta Cep, Eta Aql, and possibly T Mon. The kinematics of this component is similar to that observed in line-doubling IR spectra of Mira variables. This resemblance suggests the existence of pulsationally driven shock waves in the atmospheres of Cepheids to explain their IR line asymmetries and splitting. The systematically larger Baade-Wesselink radii derived earlier for Eta Aql and X Sgr are confirmed. The magnitude of the effect is about 20 percent. 41 refs.