International Space Science Institute

About: International Space Science Institute is a nonprofit organization based out in Bern, Switzerland. It is known for research contribution in the topics: Solar wind & Comet. The organization has 120 authors who have published 858 publications receiving 25772 citations. The organization is also known as: ISSI.

Multiwavelength Period-Luminosity and Period-Luminosity-Color relations at maximum-light for Mira variables in the Magellanic Clouds

Abstract: We present Period-Luminosity and Period-Luminosity-Color relations at maximum-light for Mira variables in the Magellanic Clouds using time-series data from the Optical Gravitational Lensing Experiment (OGLE-III) and {\it Gaia} data release 2. The maximum-light relations exhibit a scatter typically up to $\sim 30\%$ smaller than their mean-light counterparts. The apparent magnitudes of Oxygen-rich Miras at maximum-light display significantly smaller cycle-to-cycle variations than at minimum-light. High-precision photometric data for Kepler Mira candidates also exhibit stable magnitude variations at the brightest epochs while their multi-epoch spectra display strong Balmer emission lines and weak molecular absorption at maximum-light. The stability of maximum-light magnitudes for Miras possibly occurs due to the decrease in the sensitivity to molecular bands at their warmest phase. At near-infrared wavelengths, the Period-Luminosity relations of Miras display similar dispersion at mean and maximum-light with limited time-series data in the Magellanic Clouds. A kink in the Oxygen-rich Mira Period-Luminosity relations is found at 300 days in the $VI$-bands which shifts to longer-periods ($\sim 350$~days) at near-infrared wavelengths. Oxygen-rich Mira Period-Luminosity relations at maximum-light provide a relative distance modulus, $\Delta \mu = 0.48\pm0.08$~mag, between the Magellanic Clouds with a smaller statistical uncertainty than the mean-light relations. The maximum-light properties of Miras can be very useful for stellar atmosphere modeling and distance scale studies provided their stability and the universality can be established in other stellar environments in the era of extremely large telescopes.

Star clusters: Anything but simple

Abstract: The heated debate on the importance of stellar rotation and age spreads in massive star clusters has just become hotter by throwing stellar variability into the mix.

Clustering of Local Group distances: publication bias or correlated measurements? VI. Extending to Virgo cluster distances

Abstract: We have established an internally consistent Local Group distance framework, using the Galactic Center, the Large Magellanic Cloud, and Messier 31 (M31) as important stepping stones. At greater distances, few distance benchmarks are available. As a consequence, M87 and/or Virgo cluster distances are often invoked as the next rung on the ladder to more distant objects such as the Fornax and Coma clusters. Therefore, we extensively mined the published literature for independently derived distance estimates to either M87 or the center of the Virgo cluster. Based on our newly compiled, comprehensive database of 213 such distances, published between 1929 and 2017 July, we recommend an outward extension to our distance framework, $(m-M)_0^{\rm M87} = 31.03 \pm 0.14$ mag ($D = 16.07 \pm 1.03$ Mpc; where the uncertainty represents the Gaussian $\sigma$ of the distribution), based on a subset of recent (post-1990) M87/Virgo cluster distance measurements. The most stable distance tracers employed here were derived from analysis of both primary and secondary distance indicators. Among the former, we preferentially rely on Cepheid period--luminosity relations and red-giant-branch terminal magnitudes; our preferred secondary distance tracers are surface brightness fluctuations. Our updated distance modulus to M87 implies a slightly reduced black hole mass of $(5.9 \pm 0.6) \times 10^9 M_\odot$ with respect to that determined by the Event Horizon Telescope collaboration.

Collisionless mirror mode trapping

Abstract: We investigate trapping of mirror modes in a magnetic slab. This model is a simplification of a real situation in front of the magnetopause where mirror waves may become trapped in a region close to the magnetopause for tangential discontinuity conditions and an unidentified (hypothetical) boundary deeper in the sheath which we, for simplicity, assume to be another tangential discontinuity. Such magnetic slabs may trap mirror modes selecting a particular perpendicular wave lengths which follows from a quantization condition on the perpendicular wavenumber.

The VMC Survey -- XXXVII. Pulsation periods of dust enshrouded AGB stars in the Magellanic Clouds

Abstract: (abridged)Variability is a key property of stars on the asymptotic giant branch (AGB). Their pulsation period is related to the luminosity and mass-loss rate of the star. The long-period variables (LPVs) and Mira variables are the most prominent of all types of variability of evolved stars. The reddest, most obscured AGB stars are too faint in the optical and have eluded large variability surveys. Selection criteria are derived based on colour-colour and colour-magnitude diagrams from the combination of VISTA Magellanic Cloud (VMC) survey, Spitzer IRAC and AllWISE data. After eliminating LPVs with known periods shorter than 450 days, a sample of 1299 candidate obscured AGB stars is selected. K-band LCs are constructed combining the epoch photometry available in the VMC survey with literature data, analysed for variability and fitted with a single period sine curve to derive mean magnitudes, amplitudes and periods. A subset of 254 stars are either new variables, or known variables where the period we find is better determined than the literature value, or longer than 1000 days. The spectral energy distributions (SEDs) of these stars are fitted to a large number of templates. For this purpose the SEDs and Spitzer IRS spectra of some non-AGB stars are also fitted to have templates of the most likely contaminants in the sample. A sample of 217 likely LPVs is found. Thirty-four stars have periods longer than 1000 days although some of them have alternative shorter periods. Mass-loss rates and luminosities are estimated from the template fitting. Period-luminosity relations are presented for C- and O-rich Miras that appear to be extensions of relations derived in the literature for shorter periods. The fit for the C-stars is particularly well defined (with 182 objects) and reads Mbol = (-2.27 \pm 0.20) log P + (1.45 \pm 0.54)mag with an rms of 0.41 mag.