Modelling the rotation period distribution of M dwarfs in the <Emphasis Type="Italic">Kepler</Emphasis> field

McQuillan et al. (Mon. Not. R. Astron. Soc. 432:1203, 2013) presented 1570 periods \(P\) of M dwarf stars in the field of view of the Kepler telescope. It is expected that most of these reflect rotation periods, due to starspots. It is shown here that the data can be modelled as a mixture of four subpopulations, three of which are overlapping log-normal distributions. The fourth subpopulation has a power law distribution, with \(P^{-1/2}\). It is also demonstrated that the bulk of the longer periods, representing the two major subpopulations, could be drawn from a single subpopulation, but with a period-dependent probability of observing half the true period.     

A geological constraint on relative sea level in Marine Isotope Stage 3 in the Larsemann Hills, Lambert Glacier region, East Antarctica (31 366–33 228 cal yr BP)

In this paper we present geological evidence from the Larsemann Hills (Lambert Glacier – Amery Ice Shelf region, East Antarctica) of marine sediments at an altitude of c. 8 m a.s.l., as revealed by diatom, pigment and geochemical proxies in a lake sediment core. The sediments yielded radiocarbon dates between c. 26 650 and 28 750 ¹⁴C yr BP (31 366–33 228 cal yr BP). This information can be used to constrain relative sea level adjacent to the Lambert Glacier at the end of Marine Isotope Stage 3. These data are compared with the age and altitude of Marine Isotope Stage 3 marine deposits elsewhere in East Antarctica and discussed with reference to late Quaternary ice sheet history and eustatic sea-level change.     

The “four sigma” limit for significant periodicities

Most of the pulsations which have been observed in sdB stars have very low amplitudes. Detection of modes from photometric observations is usually performed by noting the most prominent peaks in a periodogram or, equivalently, an amplitude spectrum. A common strategy is to assume that peaks which exceed four times the mean noise level correspond to significant periodicities. The efficiency of the assumption is investigated by simulation. It is found that the actual significance levels corresponding to the four sigma limit may vary by orders of magnitude, depending on the exact data configuration.     

New <Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar age constraints on the Late Palaeozoic tectonic evolution of the western Tianshan (Xinjiang,northwestern China), with emphasis on Permian fluid ingress

Laser-probe dating of mylonite whole-rock samples from the North Tianshan—Main Tianshan fault zone that cross-cuts the North Tianshan domain’s southern margin yielded ⁴⁰Ar/³⁹Ar spectra with 255–285 Ma ages. Biotite from an undeformed, Early Carboniferous granite, which cuts the steep mylonitic foliation in the Proterozoic basement of the Yili arcs’s southern margin, gave a 263.4 ± 0.6 Ma plateau age (1σ). Pre-Carboniferous metasediments overlying this basement yielded plateau ages (1σ) of 253.3 ± 0.3 (muscovite) and 252.3 ± 0.3 (biotite) Ma. The Permian ages of mylonites date movement on these ductile, dextral strike-slip shear zones, whereas the mica ages are interpreted by recrystallisation as a result of fluid flow around such transcurrent faults. We propose that the Tianshan’s Permian syn-tectonic bimodal magmatism was created in a non-plume-related Yellowstone-like extensional–transtensional tectonic regime. Gold mineralisation, tracing aqueous flow in the crust, peaked in Permian time and continued locally into the Triassic. The picture is emerging that a convective fluid system partly driven by magmatic heat, existed in a strongly fractured and weakened crust with an elevated heat flow, leading to regional-scale isotope resetting. We suggest that surprisingly young isotopic ages in the literature for early orogenic (ultra)high-pressure metamorphism are similarly due to fluid-mediated recrystallisation.     

Soil temperature spin-up in land surface schemes

Land surface schemes used in atmospheric and hydrologic models require the specification of initial soil-temperature profiles. However, detailed soil temperature information is generally unavailable, hence modellers sometimes recur to specifying simplified initial conditions such as vertically constant profiles, assuming that the harmonic heating at the soil surface induces a rapid equilibrium to a steady periodic state. In this paper, using both numerical and analytical approaches, it is shown that such a transition to a steady periodic state is not always very rapid. In particular, it is demonstrated that the characteristic time required to reach equilibrium is highly dependent on the precise timing of initialisation with respect to the cycle of surface heating, and that initialising at the instant coincident with the occurrence of the maximum soil heat flux is the preferred mode.     

The analysis of indexed astronomical time series –VII. Simultaneous use of times of maxima and minima to test for period changes in long-period variables

A statistical model is formulated that enables one to analyse jointly the times between maxima and minima in the light curves of monoperiodic pulsating stars. It is shown that the combination of both sets of data into one leads to analyses that are more sensitive. Illustrative applications to the American Association of Variable Star Observers data for a number of long-period variables demonstrate the usefulness of the approach.     

Mode identification in the δ Scuti Star 1 Mon

We present new multicolour photometry and simultaneous high-dispersion spectroscopy for the δ Scuti star 1 Mon. The two main periodicities in the star are still present, but the third known period is not directly detected in the new radial velocities or light variations. However, it is detected in the periodogram of the second moment of the line profile variations. We use the cross-correlation function as an approximation for the line profile variations. By computing theoretical profiles for a given mode and comparing them with phased cross-correlation profiles, we are able to determine a goodness-of-fit criterion and estimate the most probable spherical harmonic degree,     the azimuthal order, m , of the pulsation and also the angle of inclination. We then compare the relative amplitudes and phases of the photometric variations in five wavebands and obtain the best estimates of     for the two visible periodicities. We confirm the earlier determinations that the main periodicity is a radial mode and that the other periodicity is probably         We show that the line profile variations and light variations give consistent results. We point out the importance of a long wavelength range when using the photometric mode identification technique. Finally, we attempt to match the two periods with unstable modes from linear, non-adiabatic calculations. We are able to show that the principal period is well matched by either the fundamental or first overtone radial mode, but could not find a satisfactory fit to the     mode. We discuss implications for mode identification of δ Scuti stars based on what we have learned from this star.     

Testing the bivariate series of Mira light curve rise and fall times for changes

The American Association of Variable Star Observers supplies the astronomical community with a large data base of times of light maxima and minima of Mira (long-period pulsating) stars. Period change studies using these data invariably use either times between maxima, or those between minima. A statistical analysis based on the two-component time series of light curve rise and fall times is developed. The results, which enable one to detect changes in the shapes of light curves, are applied to observations of seven long-period variables.     

Apparent partial loss age spectra of Neoarchean hornblende (Murmansk Terrane,Kola Peninsula,Russia): the role of biotite inclusions revealed by 40Ar/39Ar laserprobe analysis

Metamorphic hornblende frequently yields spectra with progressively increasing ⁴⁰Ar/³⁹Ar age steps, often interpreted as caused by partial resetting due to thermally activated radiogenic argon loss by solid‐state diffusion. Yet, in many cases rising Ca/K ratio spectra for such samples imply the presence of minor inclusions of K‐contaminant minerals. To avoid parts of grains with mineral inclusions or compositional zoning we drilled tiny discs from thin sections under a petrographic microscope. Laser step‐heating of drilled biotite‐free hornblende discs yielded flat age and ratio spectra. In contrast, furnace step‐heated hornblende separates from the same samples produced apparent loss age spectra. Moreover, biotite‐free samples yielded flat spectra by laser and furnace dating. Consequently, apparent loss spectra result from degassing of included substantially younger biotite before its hornblende host during laboratory step‐heating; c. 2640 Ma hornblende ages constrain the Murmansk Terrane's cooling.     

Near-infrared time-series photometry of six fields in the young open cluster IC 2391

Fields containing targets of spectral types later than M5 were monitored in   JHK_s   for about 7 h each. None of the targets showed variability at levels exceeding 0.02 (or smaller, in some cases). Seven new variable stars were discovered serendipitously. The large number of measurements (more than 50) of each field allows the construction of accurate colour–magnitude and colour–colour diagrams. These could be used to identify a small number of candidate very cool objects.