We present results of a study to investigate the spatial distribution of X-ray active young stellar objects near the Lupus star forming region (SFR). In this SFR, a recent study has led to the discovery of some 130 new weak-line T Tauri stars (WTTS) dispersed over a large area of some 230 square degrees. However, the true extent of the spatial distribution of these stars could not be determined in this study.
We search for new T Tauri star (TTS) candidates with the mid-infrared (MIR) part of the AKARI All-Sky Survey at 9 and 18{mu}m wavelengths. We used the point source catalogue (PSC) obtained by the Infrared Camera (IRC) on board AKARI. We combined the 2MASS PSC and the 3rd version of the USNO CCD Astrograph Catalogue (UCAC) with the AKARI IRC-PSC, and surveyed 517 known TTSs over a 1800-square-degree part of the Taurus-Auriga region to develop criteria to extract TTSs. We considered asymptotic giant branch (AGB) stars, post-AGB stars, planetary nebulae (PNe), and galaxies, which have similar MIR colours, to separate TTSs from these sources. We finally searched for new TTS candidates from AKARI IRC-PSC in the same Taurus-Auriga region. Of the 517 known TTSs, we detected 133 sources with AKARI: 46 sources were not detected by IRAS. Based on the colour-colour and colour-magnitude diagrams made from the AKARI, 2MASS, and UCAC surveys, we propose the criteria to extract TTS candidates from the AKARI All-Sky data, and 68/133 AKARI detected TTSs have passed these criteria. On the basis of our criteria, we selected 176/14725 AKARI sources as TTS candidates that are located around the Taurus-Auriga region. Comparing these sources with SIMBAD, we found that 148 are previously identified sources including 115 young stellar objects (YSOs), and 28 unidentified sources. Based on SIMBAD identifications, we infer the TTS-identification probability using our criteria to be ~75%. We find 28 TTS candidates, of which we expect ~21 to be confirmed once follow-up observations can be obtained. Although the probability of ~75% is not so high, it is affected by the completeness of the SIMBAD database, and we can search for TTSs over the whole sky, and all star-forming regions.
Dwarf galaxies are key objects for small-scale cosmological tests like the abundance problems or the planes-of-satellites problem. A crucial task is therefore to get accurate information for as many nearby dwarf galaxies as possible. Using extremely deep, groundbased V and i-band Subaru Suprime Cam photometry with a completeness of i=27mag, we measure the distance of the dwarf galaxy [TT2009] 25 using the tip of the red giant branch (RGB) as a standard candle. This dwarf resides in the field around the Milky Way-analog NGC891. Using a Bayesian approach, we measure a distance of 10.28Mpc, which is consistent with the distance of NGC891, and thus confirm it as a member of NGC891. The dwarf galaxy follows the scaling relations defined by the Local Group dwarfs. We do not find an extended stellar halo around [TT2009] 25. In the small field of view of 100kpc covered by the survey, only one bright dwarf galaxy and the giant stream are apparent. This is comparable to the Milky Way, where one bright dwarf resides in the same volume, as well as the Sagittarius stream - excluding satellites which are farther away but would be projected in the line-of-sight. It is thus imperative to survey for additional dwarf galaxies in a larger area around NGC891 to test the abundance of dwarf galaxies and compare this to the number of satellites around the Milky Way.
We analyze the deviations of transit times from a linear ephemeris for the Kepler Objects of Interest (KOI) through quarter six of science data. We conduct two statistical tests for all KOIs and a related statistical test for all pairs of KOIs in multi-transiting systems. These tests identify several systems which show potentially interesting transit timing variations (TTVs). Strong TTV systems have been valuable for the confirmation of planets and their mass measurements. Many of the systems identified in this study should prove fruitful for detailed TTV studies.
We determined new linear ephemerides of transiting exoplanets using long-cadence de-trended data from quarters Q1 to Q17 of Kepler mission. We analysed TTV diagrams of 2098 extrasolar planets. The TTVs of 121 objects were excluded (because of insufficient data-points, influence of stellar activity, etc). Finally, new linear ephemerides of 1977 exoplanets from Kepler archive are presented. The significant linear trend was observed on TTV diagrams of approximately 35% of studied exoplanets. Knowing correct linear ephemeris is principal for successful follow-up observations of transits. Residual TTV diagrams of 64 analysed exoplanets shows periodic variation, 43 of these TTV planets were not reported yet.
The Tübingen Echelle Spectrograph (TUES), designed and managed at the University of Tübingen, flew on the Orbiting and Retrievable Far and Extreme Ultraviolet Spectrograph (ORFEUS)-SPAS II space shuttle mission in 1996, returning spectra in the 900 Å to 1400 Å wavelength range. The instrument was designed to achieve a spectral resolution of /=10000 when used with an entrance aperture of 10" diameter. During the 17.7 day flight, TUES returned 239 spectra of 62 targets. Note each file contains one echelle order.
The Tübingen Echelle (TUES) obtained moderate dispersion observations (R=13,000) using an echelle grating including orders 40 - 61 from 910 - 1410 Angstroms. The instrument was designed and built by the University of Tübingen (PI: M. Grewing) and flew as one of three spectrographs on the ORFEUS/SPAS-2 mission for 14 days in November/December 1996. The instrumental resolution was about 10,000 and the effective aperture peaks at 1.3 cm2 near 1100 Angstroms. Objects were observed in a 10 arcsec entrance aperture. The wavelength calibration was established by means of interstellar molecular hydrogen lines.
The Tubingen Echelle Spectrograph (TUES), designed and managed at the University of Tubingen, flew on the Orbiting and Retrievable Far and Extreme Ultraviolet Spectrograph (ORFEUS)-SPAS II space shuttle mission in 1996, returning spectra in the 900 Angstrom to 1400 Angstrom wavelength range. The instrument was designed to achieve a spectral resolution of 10000 when used with an entrance aperture of 10" diameter. During the 17.7 day flight, TUES returned 239 spectra of 62 targets.
We report a new star formation history for the Tucana dwarf spheroidal galaxy, obtained from a new look at a deep HST/ACS colour-magnitude diagram. We combined information from the main sequence turn-off and the horizontal branch to resolve the ancient star formation rates on a finer temporal scale than previously possible. We show that Tucana experienced three major phases of star formation, two very close together at ancient times and the last one ending between 6 and 8 Gyr ago. We show that the three discrete clumps of stars on the horizontal branch are linked to the distinct episodes of star formation in Tucana. The spatial distribution of the clumps reveals that each generation of stars presents a higher concentration than the previous one. The simultaneous modelling of the horizontal branch and the main sequence turn-off also allows us to measure the amount of mass lost by red giant branch stars in Tucana with unprecedented precision, confirming dwarf spheroidals to be excellent laboratories to study the advanced evolution of low-mass stars.
Isolated local group (LG) dwarf galaxies have evolved most or all of their life unaffected by interactions with the large LG spirals and therefore offer the opportunity to learn about the intrinsic characteristics of this class of objects. Our aim is to explore the internal kinematic and metallicity properties of one of the three isolated LG early-type dwarf galaxies, the Tucana dwarf spheroidal. This is an intriguing system, as it has been found in the literature to have an internal rotation of up to 16km/s, a much higher velocity dispersion than dwarf spheroidals of similar luminosity, and a possible exception to the too-big-too-fail problem. We present the results of a new spectroscopic dataset that we procured from the Very Large Telescope (VLT) taken with the FORS2 instrument in the region of the Ca II triplet for 50 candidate red giant branch stars in the direction of the Tucana dwarf spheroidal. These yielded line-of-sight (l.o.s.) velocity and metallicity ([Fe/H]) measurements of 39 effective members that double the number of Tucana's stars with such measurements. In addition, we re-reduce and include in our analysis the other two spectroscopic datasets presented in the literature, the VLT/FORS2 sample by Fraternali et al. (2009A&A...499..121F), and the VLT/FLAMES one from Gregory et al. (2019MNRAS.485.2010G). Across the various datasets analyzed, we consistently measure a l.o.s. systemic velocity of 180+/-1.3km/s and find that a dispersion-only model is moderately favored over models that also account for internal rotation. Our best estimate of the internal l.o.s. velocity dispersion is 6.2_-1.3_^+1.6^km/s, much smaller than the values reported in the literature and in line with similarly luminous dwarf spheroidals; this is consistent with NFW halos of circular velocities <30km/s. Therefore, Tucana does not appear to be an exception to the too-big-to-fail problem, nor does it appear to reside in a dark matter halo much more massive than those of its siblings. As for the metallicity properties, we do not find anything unusual; there are hints of the presence of a metallicity gradient, but more data are needed to pinpoint its presence.
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