A Systematic Change with Time in the Size of Betelgeuse

The diameter of Betelgeuse (α Orionis) has been measured at a wavelength of 11.15 μm using the Infrared Spatial Interferometer over the past 15 years. During this 1993-2009 time period the star's size has decreased systematically by 15%

Precision near-infrared radial velocity instrumentation I: absorption gas cells

We have built and commissioned gas absorption cells for precision spectroscopic radial velocity measurements in the near-infrared in the H and K bands. We describe the construction and installation of three such cells filled with 13CH4, 12CH3D, and 14NH3 for the CSHELL spectrograph at the NASA Infrared Telescope Facility (IRTF). We have obtained their high-resolution laboratory Fourier Transform spectra, which can have other practical uses. We summarize the practical details involved in the construction of the three cells, and the thermal and mechanical control. In all cases, the construction of the cells is very affordable. We are carrying out a pilot survey with the 13CH4 methane gas cell on the CSHELL spectrograph at the IRTF to detect exoplanets around low mass and young stars. We discuss the current status of our survey, with the aim of photon-noise limited radial velocity precision. For adequately bright targets, we are able to probe a noise floor of 7 m/s with the gas cell with CSHELL at cassegrain focus. Our results demonstrate the feasibility of using a gas cell on the next generation of near-infrared spectrographs such as iSHELL on IRTF, iGRINS, and an upgraded NIRSPEC at Keck

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 (≈25-150 Myr) moving groups, the young field star ϵ 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 ∼25-50 m s-1 at ≈2.3125 μm, 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 3σ-5σ. Our method, combined with the new iSHELL spectrograph, will yield long-term RV precisions of ≲5 m s-1 in the NIR, which will allow the detection of super-Earths near the habitable zone of mid-M dwarfs

A planet within the debris disk around the pre-main-sequence star AU Microscopii

Stars and planetary system

Pendrin Modulates ENaC Function by Changing Luminal HCO3−

The epithelial Na+ channel, ENaC, and the Cl−/HCO3− exchanger, pendrin, mediate NaCl absorption within the cortical collecting duct and the connecting tubule. Although pendrin and ENaC localize to different cell types, ENaC subunit abundance and activity are lower in aldosterone-treated pendrin-null mice relative to wild-type mice. Because pendrin mediates HCO3− secretion, we asked if increasing distal delivery of HCO3− through a pendrin-independent mechanism “rescues” ENaC function in pendrin-null mice. We gave aldosterone and NaHCO3 to increase pendrin-dependent HCO3− secretion within the connecting tubule and cortical collecting duct, or gave aldosterone and NaHCO3 plus acetazolamide to increase luminal HCO3− concentration, [HCO3−], independent of pendrin. Following treatment with aldosterone and NaHCO3, pendrin-null mice had lower urinary pH and [HCO3−] as well as lower renal ENaC abundance and function than wild-type mice. With the addition of acetazolamide, however, acid-base balance as well as ENaC subunit abundance and function was similar in pendrin-null and wild-type mice. We explored whether [HCO3−] directly alters ENaC abundance and function in cultured mouse principal cells (mpkCCD). Amiloride-sensitive current and ENaC abundance rose with increased [HCO3−] on the apical or the basolateral side, independent of the substituting anion. However, ENaC was more sensitive to changes in [HCO3−] on the basolateral side of the monolayer. Moreover, increasing [HCO3−] on the apical and basolateral side of Xenopus kidney cells increased both ENaC channel density and channel activity. We conclude that pendrin modulates ENaC abundance and function, at least in part by increasing luminal [HCO3−] and/or pH