Search

We report the discovery of VVV-WIT-07, a unique and intriguing variable source presenting a sequence of recurrent dips with a likely deep eclipse in 2012 July. The object was found serendipitously in the near-IR data obtained by the VISTA Variables in the Vía Láctea (VVV) ESO public survey. Our analysis is based on VVV variability, multicolour, and proper motion (PM) data. Complementary data from the VVV eXtended survey as well as archive data and spectroscopic follow-up observations aided in the analysis and interpretation of VVV-WIT-07. A search for periodicity in the VVV K s-band light curve of VVV-WIT-07 results in two tentative periods at P  ∼ 322 d and P  ∼ 170 d. Colours and PM are consistent either with a reddened main-sequence (MS) star or a pre-MS star in the foreground disc. The near-IR spectra of VVV-WIT-07 appear featureless, having no prominent lines in emission or absorption. Features found in the light curve of VVV-WIT-07 are similar to those seen in J1407 (Mamajek's object), a pre-MS K5 dwarf with a ring system eclipsing the star or, alternatively, to KIC 8462852 (Boyajian's star), an F3 IV/V star showing irregular and aperiodic dips in its light curve. Alternative scenarios, none of which is fully consistent with the available data, are also briefly discussed, including a young stellar object, a T Tauri star surrounded by clumpy dust structure, an MS star eclipsed by a nearby extended object, a self-eclipsing R CrB variable star, and even a long-period, high-inclination X-ray binary. [ABSTRACT FROM AUTHOR]

Aims. The aim of the project is to improve our knowledge of the low-mass and low-metallicity population to investigate the influence of metallicity on the stellar (and substellar) mass function. Methods. We present the results of a photometric and proper motion search aimed at discovering ultracool subdwarfs in large-scale surveys. We employed and combined the Fifth Data Release (DR5) of the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) and the Sloan Digital Sky Survey (SDSS) Data Release 7 complemented with ancillary data from the Two Micron All-Sky Survey (2MASS), the DEep Near-Infrared Survey (DENIS) and the SuperCOSMOS Sky Surveys (SSS). Results. The SDSS DR7 vs. UKIDSS LAS DR5 search returned a total of 32 ultracool subdwarf candidates, only two of which are recognised as a subdwarf in the literature. Twenty-seven candidates, including the two known ones, were followed-up spectroscopically in the optical between 600 and 1000 nm, thus covering strong spectral features indicative of low metallicity (e.g., CaH), 21 with the Very Large Telescope, one with the Nordic Optical Telescope, and five were extracted from the Sloan spectroscopic database to assess (or refute) their low-metal content. We confirm 20 candidates as subdwarfs, extreme subdwarfs, or ultra-subdwarfs with spectral types later than M5; this represents a success rate of ≥ 60%. Among those 20 new subdwarfs, we identify two early-L subdwarfs that are very likely located within 100 pc, which we propose as templates for future searches because they are the first examples of their subclass. Another seven sources are solar-metallicity M dwarfs with spectral types between M4 and M7 without Hα emission, suggesting that they are old M dwarfs. The remaining five candidates do not have spectroscopic follow-up yet; only one remains as a bona-fide ultracool subdwarf after revision of their proper motions. We assigned spectral types based on the current classification schemes and, when possible, we measured their radial velocities. Using the limited number of subdwarfs with trigonometric parallaxes, we estimated distances ranging from ∼95 to ∼600 pc for the new subdwarfs. We provide mid-infrared photometry extracted from the WISE satellite databases for two subdwarfs and discuss their colours. Finally, we estimate a lower limit of the surface density of ultracool subdwarfs about 5000-5700 times lower than that of solar-metallicity late-M dwarfs. [ABSTRACT FROM AUTHOR]

ABSTRACT We present new MIDI interferometric and VISIR spectroscopic observations of HD 113766 and HD 172555. Additionally, we present VISIR 11-m and 18-m imaging observations of HD 113766. These sources represent the youngest (16 and 12 Myr old, respectively) debris disc hosts with emission on ≪10 au scales. We find that the disc of HD 113766 is partially resolved on baselines of 42-102 m, with variations in resolution with baseline length consistent with a Gaussian model for the disc with a full width at half-maximum (FWHM) of 1.2-1.6 au (9-12 mas). This is consistent with the VISIR observations which place an upper limit of 0.14 arcsec (17 au) on the emission, with no evidence for extended emission at larger distances. For HD 172555, the MIDI observations are consistent with complete resolution of the disc emission on all baselines of lengths 56-93 m, putting the dust at a distance of >1 au (>35 mas). When combined with limits from TReCS imaging, the dust at ∼10 m is constrained to lie somewhere in the region of 1-8 au. Observations at ∼18 m reveal extended disc emission which could originate from the outer edge of a broad disc, the inner parts of which are also detected but not resolved at 10 m, or from a spatially distinct component. These observations provide the most accurate direct measurements of the location of the dust at 1-8 au that might originate from the collisions expected during terrestrial planet formation. These observations provide valuable constraints for models of the composition of discs at this epoch and provide a foundation for future studies to examine in more detail the morphology of debris discs. [ABSTRACT FROM AUTHOR]

This paper presents a study of the envelope of the young stellar object (YSO) GGD30IR. What distinguishes this from most other YSOs is the elongated absorption feature seen in silhouette against the background emission in the Spitzer Galactic Legacy Infrared Midplane Survey Extraordinaire 8 μm Infrared Array Camera image of the region. The size and the symmetrical placement of GGD30IR in the centre of this feature suggest that it is an extended envelope, perhaps the remnant of the collapse of the GGD30 core. We have used the extinction in the envelope measured from (i) the reduction in the 8 μm background intensity and (ii) field star colour excesses, to estimate the envelope mass, obtaining values of 0.6 ± 0.2 and , respectively. To investigate the envelope further, we have obtained Australia Telescope Compact Array 3 mm continuum and HCO+ line observations of the region. The continuum emission at 3 mm arises from both a compact (unresolved; ≤730 au) core embedded in an extended envelope ∼18 000 au × 38 000 au in extent. We estimate the core mass to be 0.11 ± 0.02 . The HCO+ emission is extended in a direction perpendicular to the long axis of the envelope, suggesting it comes from an outflow. The spectral energy distribution (SED) provides a 2–24 μm spectral index, α= 1.0, which places GGD30IR in the Class I YSO category. Integrating the SED provides a luminosity of . [ABSTRACT FROM AUTHOR]

We report the results of a near-infrared survey for long-period variables in a field of view of 20× 30 arcmin2 towards the Galactic Centre (GC). We have detected 1364 variables, of which 348 are identified with those reported in Glass et al. We present a catalogue and photometric measurements for the detected variables and discuss their nature. We also establish a method for the simultaneous estimation of distances and extinctions using the period–luminosity relations for the JHKs bands. Our method is applicable to Miras with periods in the range 100–350 d and mean magnitudes available in two or more filter bands. While J band means are often unavailable for our objects because of the large extinction, we estimated distances and extinctions for 143 Miras whose H- and -band mean magnitudes are obtained. We find that most are located at the same distance to within our accuracy. Assuming that the barycentre of these Miras corresponds to the GC, we estimate its distance modulus to be , corresponding to . We have assumed the distance modulus to the Large Magellanic Cloud to be 18.45 mag, and the uncertainty in this quantity is included in the above systematic error. We also discuss the large and highly variable extinction. Its value ranges from 1.5 mag to larger than 4 mag in except towards the thicker dark nebulae and it varies in a complicated way with the line of sight. We have identified mid-infrared counterparts in the Spitzer/IRAC catalogue of Ramírez et al. for most of our variables and find that they follow rather narrow period–luminosity relations in the 3.6–8.0 μm wavelength range. [ABSTRACT FROM AUTHOR]

V4643 Sagittarii or Nova Sagittarii 2001 was discovered in outburst at 7.7 mag on 2001 February 24. Here, we present near-infrared results of this fast classical nova obtained in the early decline phase in 2001 March followed by optical observations about one month later. Subsequently, we also present near-infrared spectra taken later in the nova's evolution, about four months after the outburst, when V4643 Sgr had entered the coronal phase. The spectra in the early decline phase are dominated by emission lines of the H i Brackett series and also the Paschen β and γ lines. We study the cause of the excitation of the O i line at 1.128 μm and discuss the variation in its strength with time after outburst. We discuss the role of optical depth effects on the observed strengths of the hydrogen Brackett and Paschen lines and discuss possible reasons for the puzzling behaviour of the Brγ line strength and whether it is correlated with the O i line behaviour. An optical spectrum is presented which shows that He ii lines are the most prominent features – after H i– to be seen in early 2001 April. We present and also discuss spectra taken in 2001 June and August which prominently show coronal lines of [Si vi] and [Si vii] at 1.9641 and 2.4807 μm, respectively. [ABSTRACT FROM AUTHOR]