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During the pre-main-sequence evolution, Young Stellar Objects (YSOs) assemble most of their mass during the episodic accretion process. The rarely seen FUOr-type events are valuable laboratories to investigate the outbursting nature of YSOs. Here, we present multiwavelength detection of a high-amplitude eruptive source in the young open cluster VdBH 221 with an ongoing outburst, including optical to mid-infrared time series and near-infrared spectra. The initial outburst has an exceptional amplitude of >6.3 mag in Gaia and 4.6 mag in K s, with a peak luminosity up to 16 L⊙ and a peak mass accretion rate of 1.4 × 10−5 M⊙ yr−1. The optical to infrared spectral energy distribution of this object is consistent with a low-mass star (0.2 M⊙) with a modest extinction (A V < 2 mag). A 100-d delay between optical and infrared rising stages is detected, suggesting an outside-in origin of the instability. The spectroscopic features of this object reveal a self-luminous accretion disc, very similar to FU Orionis, with a low line-of-sight extinction. Most recently, there has been a gradual increase in brightness throughout the wavelength range, possibly suggesting an enhancement of the mass accretion rate. [ABSTRACT FROM AUTHOR]

We have performed a comprehensive search of a VISTA Variables in the Via Lactea (VVV) data base of 9.5 yr light curves for variable sources with Δ Ks ≥ 4 mag, aiming to provide a large sample of high amplitude eruptive young stellar objects (YSOs) and detect unusual or new types of infrared variable source. We find 222 variable or transient sources in the Galactic bulge and disc, most of which are new discoveries. The sample mainly comprises novae, YSOs, microlensing events, Long Period Variable stars (LPVs), and a few rare or unclassified sources. Additionally, we report the discovery of a significant population of aperiodic late-type giant stars suffering deep extinction events, strongly clustered in the Nuclear Disc of the Milky Way. We suggest that these are metal-rich stars in which radiatively driven mass loss has been enhanced by super-solar metallicity. Among the YSOs, 32/40 appear to be undergoing episodic accretion. Long-lasting YSO eruptions have a typical rise time of ∼2 yr, somewhat slower than the 6–12 month time-scale seen in the few historical events observed on the rise. The outburst durations are usually at least 5 yr, somewhat longer than many lower amplitude VVV events detected previously. The light curves are diverse in nature, suggesting that multiple types of disc instability may occur. Eight long-duration extinction events are seen wherein the YSO dims for a year or more, attributable to inner disc structure. One binary YSO in NGC 6530 displays periodic extinction events (P =59 d) similar to KH 15D. [ABSTRACT FROM AUTHOR]

During the pre-main-sequence (pre-MS) evolution stage of a star, significant amounts of stellar mass are accreted during episodic accretion events, such as multidecade FUor-type outbursts. Here, we present a near-infrared spectroscopic follow-up study of 33 high-amplitude (most with Δ Ks > 4 mag) variable sources discovered by the Vista Variables in the Via Lactea (VVV) survey. Based on the spectral features, 25 sources are classified as eruptive young stellar objects (YSOs), including 15 newly identified FUors, six with long-lasting, but EXor-like bursts of magnetospheric accretion and four displaying outflow-dominated spectra. By examining the photometric behaviours of eruptive YSOs, we found most FUor-type outbursts have higher amplitudes (Δ Ks and Δ W 2), faster eruptive time-scales and bluer infrared colours than the other outburst types. In addition, we identified seven post-MS variables apparently associated with deep dipping events and an eruptive star with deep aluminium monoxide absorption bands resembling those seen in the V838 Mon stellar merger. [ABSTRACT FROM AUTHOR]

The VISTA Variables in the Via Lactea (VVV) survey obtained near-infrared photometry towards the Galactic bulge and the southern disc plane for a decade (2010–2019). We designed a modified Lomb–Scargle method to search for large-amplitude (⁠|$\Delta K_{s, 2-98{{\ \rm per\ cent}}}$|  > 1.5 mag) mid to long-term periodic variables (P > 10 d) in the 2nd version of VVV Infrared Astrometric Catalogue (VIRAC2-β). In total, 1520 periodic sources were discovered, including 59 candidate periodic outbursting young stellar objects (YSOs), based on the unique morphology of the phase-folded light curves, proximity to Galactic H  ii regions and mid-infrared colours. Five sources are spectroscopically confirmed as accreting YSOs. Both fast-rise/slow-decay and slow-rise/fast-decay periodic outbursts were found, but fast-rise/slow-decay outbursts predominate at the highest amplitudes. The multiwavelength colour variations are consistent with a variable mass accretion process, as opposed to variable extinction. The cycles are likely to be caused by dynamical perturbations from stellar or planetary companions within the circumstellar disc. An additional search for periodic variability amongst YSO candidates in published Spitzer -based catalogues yielded a further 71 candidate periodic accretors, mostly with lower amplitudes. These resemble cases of pulsed accretion but with unusually long periods and greater regularity. The majority of other long-period variables are pulsating dusty Miras with smooth and symmetric light curves. We find that some Miras have redder W 3 − W 4 colours than previously thought, most likely due to their surface chemical compositions. [ABSTRACT FROM AUTHOR]

We report the discovery of a mid-infrared outburst in a young stellar object (YSO) with an amplitude close to 8 mag at λ ≈ 4.6 μm. WISEA J142238.82−611553.7 is one of 23 highly variable Wide-field Infrared Survey Explorer (WISE) sources discovered in a search of infrared dark clouds (IRDCs). It lies within the small IRDC G313.671−0.309 (d ≈2.6 kpc), seen by the Herschel /Hi-Gal survey as a compact massive cloud core that may have been measurably warmed by the event. Pre-outburst data from Spitzer in 2004 suggest it is a class I YSO, a view supported by observation of weak 2.12 μm H2 emission in an otherwise featureless red continuum spectrum in 2019 (6 mag below the peak in K s). Spitzer, WISE , and VISTA Variables in the Via Lactea (VVV) data show that the outburst began by 2006 and has a duration >13 yr, with a fairly flat peak from 2010 to 2014. The low pre-outburst luminosity implies a low-mass progenitor. The outburst luminosity of a few × 102 L⊙ is consistent with an accretion rate |$\dot{M} \approx 10^{-4}$|  M⊙yr−1, comparable to a classical FU Orionis event. The 4.6 μm peak in 2010 implies T = 800–1000 K and a disc radial location R ≈ 4.5 au for the emitting region. The colour evolution suggests subsequent progression outwards. The apparent absence of the hotter matter expected in thermal instability or MRI models may be due to complete obscuration of the innermost disc, e.g. by an edge-on disc view. Alternatively, disc fragmentation/infalling fragment models might more naturally explain a mid-infrared peak, though this is not yet clear. [ABSTRACT FROM AUTHOR]

A search of the first Data Release of the VISTA Variables in the Via Lactea (VVV) Survey discovered the exceptionally red transient VVV-WIT-01 (H − Ks  = 5.2). It peaked before March 2010, then faded by ∼9.5 mag over the following 2 yr. The 1.6–22  μ m spectral energy distribution in March 2010 was well fit by a highly obscured blackbody with T ∼ 1000 K and |$A_{K_s} \sim 6.6$|  mag. The source is projected against the Infrared Dark Cloud (IRDC) SDC G331.062−0.294. The chance projection probability is small for any single event (p ≈ 0.01–0.02), which suggests a physical association, e.g. a collision between low mass protostars. However, blackbody emission at T ∼ 1000 K is common in classical novae (especially CO novae) at the infrared peak in the light curve due to condensation of dust ∼30–60 d after the explosion. Radio follow-up with the Australia Telescope Compact Array detected a fading continuum source with properties consistent with a classical nova but probably inconsistent with colliding protostars. Considering all VVV transients that could have been projected against a catalogued IRDC raises the probability of a chance association to p  = 0.13–0.24. After weighing several options, it appears likely that VVV-WIT-01 was a classical nova event located behind an IRDC. [ABSTRACT FROM AUTHOR]

We present a catalogue of 618 high-amplitude infrared variable stars (1 < ΔK < 5mag) detected by the two widely separated epochs of 2.2 μm data in the UKIDSS Galactic plane survey, from searches covering ~1470 deg2. Most were discovered by a search of all fields at 30 < l < 230°. Sources include new dusty Mira variables, three new cataclysmic variable candidates, a blazar and a peculiar source that may be an interacting binary system. However, ~60 per cent are young stellar obbjects (YSOs), based on spatial association with star-forming regions at distances ranging from 300 pc to over 10 kpc. This confirms our initial result in Contreras Peña et al. (Paper I) that YSOs dominate the high-amplitude infrared variable sky in the Galactic disc. It is also supported by recently published VISTA Variables in the Via Lactea (VVV) results at 295 < l < 350°. The spectral energy distributions of the YSOs indicate class I or flat-spectrum systems in most cases, as in the VVV sample. A large number of variable YSOs are associated with the Cygnus X complex and other groups are associated with the North America/Pelican nebula, the Gemini OB1 molecular cloud, the Rosette complex, the Cone nebula, theW51 star-forming region and the S86 and S236 HII regions. Most of the YSO variability is likely due to variable/episodic accretion on time-scales of years, albeit usually less extreme than classical FUors and EXors. Luminosities at the 2010 Wide-field Infrared Survey Explorer epoch range from ~0.1 to 103 L☉ but only rarely exceed 102.5 L☉. [ABSTRACT FROM AUTHOR]

We present the discovery of 816 high-amplitude infrared variable stars (ΔKs > 1 mag) in 119 deg2 of the Galactic mid-plane covered by the VISTA Variables in the Via Lactea (VVV) survey. Almost all are new discoveries and about 50 per cent are young stellar objects (YSOs). This provides further evidence that YSOs are the commonest high-amplitude infrared variable stars in the Galactic plane. In the 2010-2014 time series of likely YSOs, we find that the amplitude of variability increases towards younger evolutionary classes (class I and flatspectrum sources) except on short time-scales (<25 d) where this trend is reversed. Dividing the likely YSOs by light-curve morphology, we find 106 with eruptive light curves, 45 dippers, 39 faders, 24 eclipsing binaries, 65 long-term periodic variables (P > 100 d) and 162 shortterm variables. Eruptive YSOs and faders tend to have the highest amplitudes and eruptive systems have the reddest spectral energy distribution (SEDs). Follow-up spectroscopy in a companion paper verifies high accretion rates in the eruptive systems. Variable extinction is disfavoured by the two epochs of colour data. These discoveries increase the number of eruptive variable YSOs by a factor of at least 5, most being at earlier stages of evolution than the known FUor and EXor types. We find that eruptive variability is at least an order of magnitude more common in class I YSOs than class II YSOs. Typical outburst durations are 1-4 yr, between those of EXors and FUors. They occur in 3-6 per cent of class I YSOs over a 4 yr time span. [ABSTRACT FROM AUTHOR]

In a companion work (Paper I), we detected a large population of highly variable Young Stellar Objects (YSOs) in the Vista Variables in the Via Lactea (VVV) survey, typically with class I or flat spectrum spectral energy distributions and diverse light-curve types. Here we present infrared spectra (0.9-2.5 μm) of 37 of these variables, many of them observed in a bright state. The spectra confirm that 15/18 sources with eruptive light curves have signatures of a high accretion rate, either showing EXor-like emission features (Δv = 2 CO, Brγ ) and/or FUor-like features (Δv = 2 CO and H2O strongly in absorption). Similar features were seen in some long-term periodic YSOs and faders but not in dippers or short-term variables. The sample includes some dusty Mira variables (typically distinguished by smooth Mira-like light curves), two cataclysmic variables and a carbon star. In total, we have added 19 new objects to the broad class of eruptive variable YSOs with episodic accretion. Eruptive variable YSOs in our sample that were observed at bright states show higher accretion luminosities than the rest of the sample. Most of the eruptive variables differ from the established FUor and EXor subclasses, showing intermediate outburst durations and a mixture of their spectroscopic characteristics. This is in line with a small number of other recent discoveries. Since these previously atypical objects are now the majority amongst embedded members of the class, we propose a new classification for them as MNors. This term (pronounced emnor) follows V1647 Ori, the illuminating star of McNeil's Nebula. [ABSTRACT FROM AUTHOR]

Analysis of T dwarfs using model atmospheres has been hampered by the absence of reliable line lists for methane and ammonia. Newly computed high-temperature line lists for both of these important molecules are now available, so it is timely to investigate the appearance of the various absorption features in T dwarfs in order to better understand their atmospheres and validate the new line lists. We present high-quality R ∼ 5000 Gemini/NIFS 1.0-2.4 μm spectra of the T8 standard 2MASS 0415-0935 and the T9 standard UGPS 0722-0540. We use these spectra to identify numerous methane and ammonia features not previously seen and we discuss the implications for our understanding of T dwarf atmospheres. Among our results, we find that ammonia is the dominant opacity source between ∼1.233-1.266 μm in UGPS 0722-0540, and we tentatively identify several absorption features in this wavelength range in the T9's spectrum which may be due entirely to ammonia opacity. Our results also suggest that water rather than methane is the dominant opacity source in the red half of the J band of the T8 dwarf. Water appears to be the main absorber in this wavelength region in the T9 dwarf until ∼1.31 μm, when methane starts to dominate. [ABSTRACT FROM AUTHOR]

Analysis of T dwarfs using model atmospheres has been hampered by the absence of reliable line lists for methane and ammonia. Newly computed high-temperature line lists for both of these important molecules are now available, so it is timely to investigate the appearance of the various absorption features in T dwarfs in order to better understand their atmospheres and validate the new line lists. We present high-quality R ~ 5000 Gemini/NIFS 1.0-2.4 μm spectra of the T8 standard 2MASS 0415-0935 and the T9 standard UGPS 0722-0540. We use these spectra to identify numerous methane and ammonia features not previously seen and we discuss the implications for our understanding of T dwarf atmospheres. Among our results, we find that ammonia is the dominant opacity source between ~ 1.233-1.266 μm in UGPS 0722-0540, and we tentatively identify several absorption features in this wavelength range in the T9's spectrum which may be due entirely to ammonia opacity. Our results also suggest that water rather than methane is the dominant opacity source in the red half of the J band of the T8 dwarf. Water appears to be the main absorber in this wavelength region in the T9 dwarf until ~1.31 μm, when methane starts to dominate. [ABSTRACT FROM AUTHOR]

The new generation of IR surveys are revealing and quantifying Galactic features that provide an improved 3D interpretation of our own Galaxy. We present an analysis of the global distribution of dust clouds in the bulge using the near-IR photometry of 157 million stars from the VVV survey. We investigate the color-magnitude diagram of the Milky Way bulge, which shows a red giant clump of core He burning stars that is split into two color components, with a mean color difference of (Z - Ks) = 0.55 mag that is equivalent to AV = 2.0 mag. We conclude that there is an optically thick dust lane at intermediate latitudes above and below the plane that stretches across several square degrees from l = -10° to l = +10°.We call this feature the great dark lane. Although its exact distance is uncertain, it is located in front of the bulge. The evidence for a large-scale great dark lane within the Galactic bulge is important for constraining models of the barred Milky Way bulge and for comparing our galaxy with external barred galaxies in which these types of features are prominent. We discuss two other potential implications of the great dark lane for microlensing and bulge stellar populations studies. [ABSTRACT FROM AUTHOR]

The UKIDSS Galactic Plane Survey (GPS) began in 2005 as a seven year effort to survey ∼1800 deg2 of the northern Galactic plane in the J, H, and K passbands. The survey included a second epoch of K-band data, with a baseline of two to eight years, for the purpose of investigating variability and measuring proper motions. We have calculated proper motions for 167 million sources in a 900 deg2 area located at l > 60° in order to search for new high proper motion objects. Visual inspection has verified 617 high proper motion sources (>200 mas yr−1) down to K = 17, of which 153 are new discoveries. Among these, we have a new spectroscopically confirmed T5 dwarf, an additional T dwarf with estimated type T6, 13 new L dwarf candidates, and two new common proper motion systems containing ultracool dwarf candidates. We provide improved proper motions for an additional 12 high proper motion stars that were independently discovered in the WISE data set during the course of this investigation. [ABSTRACT FROM PUBLISHER]

We have carried out a search for late-type T dwarfs in the UKIRT Infrared Deep Sky Survey Galactic Plane Survey 6th Data Release. The search yielded two persuasive candidates, both of which have been confirmed as T dwarfs. The brightest, UGPS J0521+3640, has been assigned the spectral type T8.5 and appears to lie at a distance of 7-9 pc. The fainter of the two, UGPS J0652+0324, is classified as a T5.5 dwarf and lies at an estimated distance of 28-37 pc. Warm- Spitzer observations in IRAC channels 1 and 2, taken as part of the GLIMPSE360 Legacy Survey, are available for UGPS J0521+3640 and we used these data with the near-infrared spectroscopy to estimate its properties. We find best-fitting solar metallicity BT-Settl models for and 650 K and and 5.0. These parameters suggest a mass between 14 and for an age between 1 and 5 Gyr. The proximity of this very cool T dwarf, and its location in the Galactic plane, makes it an ideal candidate for high-resolution adaptive optics imaging to search for cool companions. [ABSTRACT FROM AUTHOR]

We report the discovery of a very cool, isolated brown dwarf, UGPS 05, with the United Kingdom Infrared Telescope Deep Sky Survey (UKIDSS) Galactic Plane Survey. The near-infrared spectrum displays deeper H2O and CH4 troughs than the coolest known T dwarfs and an unidentified absorption feature at 1.275 μm. We provisionally classify the object as a T10 dwarf but note that it may in future come to be regarded as the first example of a new spectral type. The distance is measured by trigonometric parallax as , making it the closest known isolated brown dwarf. With the aid of Spitzer/Infrared Array Camera (IRAC) we measure = 4.71. It is the coolest brown dwarf presently known - the only known T dwarf that is redder in is the peculiar T7.5 dwarf SDSS J1416+13B, which is thought to be warmer and more luminous than UGPS 05. Our measurement of the luminosity, aided by Gemini/T-ReCS N-band photometry, is . Using a comparison with well-studied T8.5 and T9 dwarfs we deduce . This is supported by predictions of the Saumon & Marley models. With apparent magnitude , UGPS 05 is the brightest of the ∼90 T dwarfs discovered by UKIDSS so far. It offers opportunities for future study via high-resolution near-infrared spectroscopy and spectroscopy in the thermal infrared. [ABSTRACT FROM AUTHOR]

We report observations of the linear polarization of a sample of 49 nearby bright stars measured to sensitivities of between ∼1 and . The majority of stars in the sample show measurable polarization, but most polarizations are small with 75 per cent of the stars having . Correlations of the polarization with distance and position indicate that most of the polarization is of interstellar origin. Polarizations are small near the galactic pole and larger at low-galactic latitudes, and the polarization increases with distance. However, the interstellar polarization is very much less than would be expected based on polarization–distance relations for distant stars showing that the solar neighbourhood has little interstellar dust. BS 3982 (Regulus) has a polarization of , which is most likely due to electron scattering in its rotationally flattened atmosphere. BS 7001 (Vega) has polarization at a level of which could be due to scattering in its dust disc, but is also consistent with interstellar polarization in this direction. The highest polarization observed is that of BS 7405 (α Vul) with a polarization of 0.13 per cent. [ABSTRACT FROM AUTHOR]

We present very sensitive polarimetry of 55 Cnc and τ Boo in an attempt to detect the partially polarized reflected light from the planets orbiting these two stars. 55 Cnc is orbited by a hot Neptune planet (55 Cnc e) at 0.038 au, a hot Jupiter planet (55 Cnc b) at 0.11 au and at least three more distant planets. The polarization of this system is very stable, showing no sign of the periodic variations that would be expected if a short-period planet were detected. The measured standard deviation of the nightly averaged Stokes Q/ I and U/ I parameters is . We derive upper limits on the geometric albedo, AG, and planetary radius using Monte Carlo multiple scattering simulations of a simple model atmosphere. We assume Rayleigh-like scattering and polarization behaviour (scaled by the maximum polarization, pm, at 90°) and pressure insensitive extinction. Atmospheres in which multiple scattering plays only a small role have an almost linear relation between polarization and AG. In this case, the 4σ upper limit is for 55 Cnc e. This is most easily explained if 55 Cnc e is relatively small, like GJ 436b, and therefore not a pure H–He planet. The data do not provide a useful upper limit for 55 Cnc b. τ Boo is orbited by an unusually massive hot Jupiter planet. The data show a standard deviation in the night-to-night average Stokes Q/ I and U/ I polarization parameters of . The 4σ upper limit is for τ Boo b, adopting the fairly well established orbital inclination . This extends the similar upper limits reported previously for this planet to longer wavelengths. The fact that the τ Boo data show more scatter, despite the smaller photon noise for this bright star, may be due to the spot activity detected photometrically by the Microvariability & Oscillations of Stars ( MOST) satellite. These results contrast markedly with the recent claim of a 3σ detection of a periodic polarization signal from HD 189733 with amplitude , attributed to the planet HD 189733 b. [ABSTRACT FROM AUTHOR]

We present near-infrared long-slit and multislit spectra of low-mass brown dwarf candidates in the Orion nebula cluster. The long-slit data were observed in the H and K bands using NIRI on the Gemini-North Telescope. The multi-object spectroscopic observations were made using IRIS2 on the Anglo-Australian Telescope at H band. We develop a spectral typing scheme based on optically calibrated, near-infrared spectra of young sources in the Taurus and IC 348 star-forming regions with spectral types M3.0 to M9.5. We apply our spectral typing scheme to 52 sources, including previously published UKIRT and GNIRS spectra. 40 objects show strong water absorption with spectral types of M3 to >M9.5. The latest type objects are provisionally classified as early L types. We plot our sources on Hertzsprung–Russell diagrams overlaid with theoretical pre-main-sequence isochrones. The majority of our objects lie close to or above the 1-Myr isochrone, leading to an average cluster age that is <1 Myr. We find 38 sources lie at or below the hydrogen-burning limit . 10 sources potentially have masses below the deuterium-burning limit . We use a Monte Carlo approach to model the observed luminosity function with a variety of cluster age and mass distributions. The lowest values are produced by an age distribution centred at 1 Myr, with a mass function that declines at substellar masses according to an power law in the range . We find that truncating the mass function at produces luminosity functions that are starved of the faintest magnitudes, even when using bimodal age populations that contain 10-Myr-old sources. The results of these Monte Carlo simulations therefore support the existence of a planetary mass population in the ONC. [ABSTRACT FROM AUTHOR]

The UKIDSS Galactic Plane Survey (GPS) is one of the five near-infrared Public Legacy Surveys that are being undertaken by the UKIDSS consortium, using the Wide Field Camera on the United Kingdom Infrared Telescope. It is surveying 1868 deg2 of the northern and equatorial Galactic plane at Galactic latitudes in the J, H and K filters and a ∼200-deg2 area of the Taurus–Auriga–Perseus molecular cloud complex in these three filters and the 2.12 μm (1–0) H2 filter. It will provide data on sources. Here we describe the properties of the data set and provide a user's guide for its exploitation. We also present brief Demonstration Science results from DR2 and from the Science Verification programme. These results illustrate how GPS data will frequently be combined with data taken in other wavebands to produce scientific results. The Demonstration Science comprises six studies. (1) A GPS- Spitzer-GLIMPSE cross-match for the star formation region G28.983−0.603 to identify YSOs. This increases the number of YSOs identified by a factor of 10 compared to GLIMPSE alone. (2) A wide-field study of the M17 nebula, in which an extinction map of the field is presented and the effect of source confusion on luminosity functions in different subregions is noted. (3) H2 emission in the ρ Ophiuchi dark cloud. All the molecular jets are traced back to a single active clump containing only a few protostars, which suggests that the duration of strong jet activity and associated rapid accretion in low-mass protostars is brief. (4) X-ray sources in the nuclear bulge. The GPS data distinguishes local main-sequence counterparts with soft X-ray spectra from nuclear bulge giant counterparts with hard X-ray spectra. (5) External galaxies in the zone of avoidance. The galaxies are clearly distinguished from stars in fields at longitudes . (6) IPHAS-GPS optical–infrared spectrophotometric typing. The versus diagram is used to distinguish A–F type dwarfs, G dwarfs, K dwarfs and red clump giants in a field with high reddening. [ABSTRACT FROM AUTHOR]

Background: Various bone resorption markers in humans are useful for supporting the diagnosis of malignant skeletal pathology, with certain bone resorption markers appearing to be more discriminatory for detecting cancer-induced osteolysis than others. Canine osteosarcoma (OSA) is characterized by focal bone destruction, but a systematic investigation for determining which bone resorption marker best supports the diagnosis of OSA in dogs has not been reported. Hypothesis: Dogs with OSA will have increased concentrations of bone resorption markers compared with healthy dogs and dogs with orthopedic disorders. Differences will exist among various bone resorption markers for their ability to support the diagnosis of malignant osteolysis in dogs with OSA. Animals: Single time point, cross-sectional, cohort study including dogs with OSA (n = 20) or orthopedic disorders (n = 20) and healthy dogs (n = 22). Methods: Basal concentrations of urine and serum N-telopeptide (NTx), urine and serum C-telopeptide (CTx), and urine deoxypyridinoline (DPD) were compared among all 3 groups. Results: Compared with healthy dogs and dogs with orthopedic disorders, urine NTx, serum NTx, and serum CTx concentrations were significantly increased in dogs with OSA. For urine NTx and serum NTx, the calculated lower and upper 95% confidence limits in dogs with OSA did not overlap with dogs diagnosed with orthopedic disorders or healthy dogs. Conclusions and clinical importance: Of the markers evaluated in this study, urine NTx and serum NTx appear to be the most discriminatory resorption markers supporting the diagnosis of focal malignant osteolysis in dogs with OSA. [ABSTRACT FROM AUTHOR]

The results of a near-infrared ( J H K LP) imaging linear polarimetry survey of 20 young stellar objects (YSOs) in ρ Ophiuchi are presented. The majority of the sources are unresolved, with K-band polarizations, P K < 6 per cent. Several objects are associated with extended reflection nebulae. These objects have centrosymmetric vector patterns with polarization discs over their cores; maximum polarizations of P K > 20 per cent are seen over their envelopes. Correlations are observed between the degree of core polarization and the evolutionary status inferred from the spectral energy distribution. K-band core polarizations >6 per cent are only observed in Class I YSOs. A 3D Monte Carlo model with oblate grains aligned with a magnetic field is used to investigate the flux distributions and polarization structures of three of the ρ Oph YSOs with extended nebulae. A ρ∝ r−1.5 power law for the density is applied throughout the envelopes. The large-scale centrosymmetric polarization structures are due to scattering. However, the polarization structure in the bright core of the nebula appears to require dichroic extinction by aligned non-spherical dust grains. The position angle indicates a toroidal magnetic field in the inner part of the envelope. Since the measured polarizations attributed to dichroic extinction are usually ≤10 per cent, the grains must either be nearly spherical or very weakly aligned. The higher polarizations observed in the outer parts of the reflection nebulae require that the dust grains responsible for scattering have maximum grain sizes ⩽1.05 μm. [ABSTRACT FROM AUTHOR]

We report the results of near infrared spectroscopy of 11 luminosity-selected candidate planetary mass objects (PMOs) in the Trapezium Cluster with Gemini South/Gemini Near-Infrared Spectrograph and Gemini North/Near-Infrared Imager. Six have spectral types ≥M9, in agreement with expectations for PMOs. Two have slightly earlier types, and three are much earlier types which are probably field stars. Four of the six sources with types ≥M9 have pseudo-continuum profiles which confirm them as low gravity cluster members. The gravity status of the other cool dwarfs is less clear but these remain candidate PMOs. The derived number fraction of PMOs with is 1–14 per cent, these broad limits reflecting the uncertainty in source ages. However, the number fraction with is at least 5 per cent. These detections add significantly to the body of evidence that a planetary mass population is produced by the star formation process. [ABSTRACT FROM AUTHOR]

Primate species often eat foods of different physical properties. This may have implications for tooth structure and wear in those species. The purpose of this study was to examine the mechanical defenses of leaves eaten by Alouatta palliata from different social groups at Hacienda La Pacifica in Costa Rica. Leaves were sampled from the home-ranges of groups living in different microhabitats. Specimens were collected during the wet and dry seasons from the same tree, same plant part, and same degree of development as those eaten by the monkeys. The toughness of over 300 leaves was estimated using a scissors test on a Darvell mechanical tester. Toughness values were compared between social groups, seasons, and locations on the leaves using ANOVA. Representative samples of leaves were also sun-dried for subsequent scanning electron microscopy and energy dispersive x-ray (EDX) analyses in an attempt to locate silica on the leaves. Both forms of mechanical defense (toughness and silica) were found to be at work in the plants at La Pacifica. Fracture toughness varied significantly by location within single leaves, indicating that measures of fracture toughness must be standardized by location on food items. Monkeys made some food choices based on fracture toughness by avoiding the toughest parts of leaves and consuming the least tough portions. Intergroup and seasonal differences in the toughness of foods suggest that subtle differences in resource availability can have a significant impact on diet and feeding in Alouatta palliata. Intergroup differences in the incidence of silica on leaves raise the possibility of matching differences in the rates and patterns of tooth wear. [ABSTRACT FROM AUTHOR]

We report the results of a deep near-infrared ( JHK) survey of the outer parts of the Trapezium Cluster with Gemini South/Flamingos. 396 sources were detected in a 26 arcmin2 area, including 138 brown dwarf candidates, defined as for an assumed age of 1 Myr. Only 33 of the brown dwarf candidates are planetary mass candidates with estimated masses in the range . In an extinction-limited sample complete to approximately (5 MJup) the mass function appears to drop by a factor of 2 at the deuterium burning threshold, i.e. at planetary masses. After allowing for background contamination it is likely that planetary mass objects at 3–13 MJup number <10 per cent of the cluster population, with an upper limit of 13 per cent. Analysis of the spatial distribution of stars and brown dwarf candidates suggests that brown dwarfs and very low-mass stars are less likely than more massive stars to have wide (>150 au) binary companions. This result has modest statistical significance (96 per cent) in our data but is supported at 93 per cent confidence by analysis of a completely independent sample taken from the Subaru data of Kaifu et al. There is a statistically very significant excess of both stars and brown dwarfs with small separations from each other (<6 arcsec or 2600 au). This appears to be due to the presence of small- N subgroups, which are likely to be dynamically unstable in the long term. Hence these results are consistent with the ‘ejected stellar embryo’ hypothesis for brown dwarf formation. We also report the discovery of two new bipolar nebulae, which are interpreted as Class I protostars. [ABSTRACT FROM AUTHOR]

We present high-quality near-infrared imaging polarimetry of HL Tau at 0.4–0.6 arcsec resolution, obtained with Subaru/CIAO and UKIRT/IRCAM. Three-dimensional Monte Carlo modelling with aligned oblate grains is used to probe the structure of the circumstellar envelope and the magnetic field, as well as the dust properties. At the J band, the source shows a centrosymmetric pattern dominated by scattered light. In the H and K bands, the central source becomes visible and its polarization appears to be dominated by dichroic extinction, with a position angle inclined by &assymp;40° to the disc axis. The polarization pattern of the environs on scales up to 200 au is consistent with the same dichroic extinction signature superimposed on the centrosymmetric scattering pattern. These data can be modelled with a magnetic field which is twisted on scales from tens to hundreds of au, or alternatively by a field which is globally misaligned with the disc axis. A unique solution to the field structure will require spatially resolved circular polarization data. The best-fitting Monte Carlo model indicates a shallow near-infrared extinction law. When combined with the observed high polarization and non-negligible albedo, these constraints can be fitted with a grain model involving dirty water ice mantles in which the largest particles have radii slightly in excess of 1 μm. The best-fitting model has an envelope structure which is slightly flattened on scales up to several hundred au. Both lobes of the bipolar outflow cavity contain a substantial optical depth of dust (not just within the cavity walls). Curved, approximately parabolic, cavity walls fit the data better than a conical cavity. The small inner accretion disc observed at millimetre wavelengths is not seen at this spatial resolution. [ABSTRACT FROM AUTHOR]

Reports on the development of a method to detect the infrared spectroscopic signature of 'hot Jupiter' planets. Signal-to-noise ratio; Contrast ratio between planet and star; Strength of water absorption.

Summary The breakdown of food in the mouth during mastication can be described in terms of two parameters: a breakage function, which describes the fragmentation of food after a bite, and a selection function which defines the probability of particle fracture. The non-zero value of the selection function depends on the manipulation of food particles by the tongue. Little, however, is known about this. As a first step, this study investigated the manipulation of wax sheets of differing sizes and shapes by the tongue after ingestion. It was found that subjects tended to orientate rectangular and square wax wafers so that the long axis of the particle was parallel to the tooth row, independent of the initial orientation given when they were introduced into the mouth. Circular wafers were randomly oriented relative to initial orientation. If this could be extrapolated to the start of mastication, then it suggests that the tongue tends to align food particles so that the post-canines produce close to the greatest surface area possible by fragmenting them along their longest axis. [ABSTRACT FROM AUTHOR]

Many plant foods contain tannins, compounds that bind proteins, such as mammalian enzymes. Although described as tasteless, tannins can be detected orally by their astringency. However, the actual mechanism of oral detection and the effect of tannins on mastication and swallowing have been little investigated. Here, we show from in vitro tests that tannic acid, a common standard in tests used to detect tannins, significantly reduces the lubricating qualities of human saliva both by decreasing its viscosity and increasing friction, both factors lending support to the notion that astringency is a tactile phenomenon. From the literature, it is clear that this effect depends on the presence of salivary proline-rich proteins (PRP). In a mammalian context, ingestion of tannin-rich foods in a species with salivary PRP will be signalled by interference with bolus formation during mastication while the increase in friction may also be detectable and lead to increased tooth wear if the signal is ignored. In a human context, cross-cultural preferences for tannin-rich beverages such as tea, coffee and red wine at the end of meals may be explained by reduction in adhesion of food particles to the oral mucosa allowing their rapid oral clearance. [ABSTRACT FROM AUTHOR]

We report the results of a survey of low-mass Class I protostars in the cm continuum. In the initial survey, seven sources in the Taurus star formation region were observed with the VLA at 0.25‐arcsec resolution. All seven sources drive CO outflows and display Herbig–Haro flows in the optical or near-infrared (NIR) wavebands. Four out of seven sources were detected, two of which are new discoveries in systems of very low luminosity, one being the lowest luminosity system detected to date in the cm continuum. Notably, three sources were not detected to a 3σ limit of 0.10 mJy/beam, which indicates that significant cm continuum emission is not a universal feature of Class I systems with outflow activity. Subsequent observations of HH30, a more evolved Class II system, found no emission to a 3σ limit of 0.03 mJy/beam. After comparison with near infrared data, we suggest that the discriminating feature of the detected systems is a relatively high ionization fraction in the stellar wind. Temporal variability of the outflow may also play a role: only recently ejected knots may have sufficiently dense plasma to be optically thick to free–free emission, and hence produce detectable flux. The one relatively bright source, IRAS 04016+2610 (L1489 IRS), is clearly resolved on a 0.4‐arcsec scale at 2 and 3.5 cm. Additional imaging with MERLIN did not detect this source with a 0.04‐arcsec beam, indicating that the radio emission is generated in a region with a radius of ≈25 au, which is broadly similar to the radius of the bipolar cavities inferred from models of NIR data. Interpretation of this system is complicated by the existence of a quadrupolar outflow, i.e. two bipolar outflows along roughly perpendicular axes, which we originally detected through polarimetric imaging. We present an NIR H[sub 2] image in which a bow shock in the secondary outflow is clearly seen. This complicated structure may have been caused by a gravitational interaction between two protostars. [ABSTRACT FROM AUTHOR]

The abilities of thirty-two complete denture wearers and thirty-two dentate subjects to break down raw carrot particles were compared. The particle size distributions produced were broader in those subjects that broke down food rapidly per chew and, conversely, narrower in those that were slower. This did not appear to depend on dental status. An analysis of mastication as composed of two separable processes, one describing the means by which particles come to be broken (selection) and the other, the size distributions of a particle upon fracturing (breakage), indicated that both processes were variable. It is concluded that no qualitative differences in the manner by which the two groups reduce food is apparent. To support this, a small study on dentate subjects suggests the covering of the palatal mucosa with an acrylic plate does not affect masticatory performance. [ABSTRACT FROM AUTHOR]

A small study on fifteen subjects found that brazil nut particles always broke down much more rapidly per chew than raw carrot particles. Both foods were swallowed, on average, after similar numbers of chews. However, a relationship was found which suggested that subjects that swallowed after few chews took less for carrots than brazils and vice versa for those that took more chews. An extended study with carrot showed a significant correlation between the rate of size breakdown and the number of chews required for swallowing in dentate subjects (r = 0.69) but not in full denture wearers. The whole sample (n = 79 including six wearers of partial dentures) gave a significant correlation of r = 0.65. It is concluded that some consideration of the physical properties (texture) of foods is necessary before results from this type of study can be interpreted as relevant or not for dentistry. [ABSTRACT FROM AUTHOR]

It has been argued that the prolonged retention of cusps in the human dentition is a relatively recent aberration due to the negligible abrasiveness of modern diets and that to achieve maximum efficiency and freedom from disease human teeth should be worn down as they are in many herbivorous mammals. Here we critically review the evidence that has been put forward to support this idea and, after discussing the design of occlusal surfaces in relation to the wide variety of mammalian diets, we conclude that cusps are adaptations for breaking food with specific physical properties. [ABSTRACT FROM AUTHOR]

The fracture toughness of sun-leaves of 42 tropical tree species growing in Singapore was measured along a 'least tough' path using an instrumented cutting technique. Punch-and-die (penetrometer) tests were also conducted. Intercostal material was analyzed for crude fibre and crude protein (total nitrogen concentration × 6.25) and the ratio of the two, the index of selerophylly, calculated for each species. Leaf anatomy was examined and specific leaf area was calculated. Thirty-seven of the species were from three definable plant communities, namely mangroves, trema belukar (secondary forest on undegraded sites) and adinandra belukar (secondary forest on highly degraded soils). There was a highly significant positive correlation between fracture toughness and index of selerophylly for the 42 species (R2 = 0.43, P < 0001) brought about largely by a high correlation between toughness and crude fibre content. Fracture toughness was not correlated with lamina tissue dorsi-ventral thickness but high toughness was clearly associated with the presence of sclerenchyma bundle sheaths and sheath extensions. Analysis of the fracture path for 26 leaves of ten mangrove species showed a high correlation between the area fraction occupied by veins and fracture toughness if one species, Avicenmia rumphiana, was excluded. The regression equation for the other nine species gave estimates of the fracture toughness of vein tissue and lamina matrix of 6053 and 327 J m-2 respectively. Punch-and-die test results only correlated well with the cutting tests when values were divided by lamina thickness. [ABSTRACT FROM AUTHOR]

Two-year-old seedlings of Sitka spruce [Picea sitchensis (Bong) Carr.] were exposed to < 5, 70, 120 and 170 nI l -1 O3 for 7 h day-1 in large ventilated glasshouses during the summer of 1986. Relative growth rates (RGR) were calculated at intervals throughout the summer and autumn using a non-destructive technique in which measurements of stem height and diameter were used to estimate above-ground biomass. No statistically significant effects of the ozone on growth were apparent during or after the period of fumigation, and growth of the seedlings had largely been completed by the end of August. The winter hardiness of these plants was subsequently tested on 10 November and 8 December by subjecting detached shoots to a range of carefully regulated freezing temperatures in controlled environment chambers. The results for the samples taken on the earlier date suggested that plants exposed to ozone were more sensitive to frost than the controls, and that this effect was dependent on the concentration of the pollutant. In the samples taken later, all the shoots appeared to have hardened equally to freezing temperatures in excess of about -20 °C. The results suggest that early autumn frosts might be damaging to Sitka spruce after exposure to high ozone Concentrations in summer. [ABSTRACT FROM AUTHOR]

The growing number of multi-epoch optical and infrared sky surveys are uncovering unprecedented numbers of new variable stars, of an increasing number of types. The short interval between observations in adjacent near-infrared filters in the UKIDSS Galactic Plane Survey (UGPS) allows for the discovery of variability on the time-scale of minutes. We report on the nature of one such object, through the use of optical spectroscopy, time series photometry, and targeted X-ray observations. We propose that UGPS J194310.32+183851.8 is a magnetic cataclysmic variable star of novel character, probably featuring a longer than average spin period and an orbital period likely to be shorter than the period gap (i.e. P orb < 2 h). We reason that the star is likely a member of the short-period intermediate-polar subclass that exists below this period boundary, but with the additional feature that system's spectral energy distribution is fainter and redder than other members of the group. [ABSTRACT FROM AUTHOR]

The 'VISTA Variables in the Vía Láctea eXtended (VVVX)' ESO Public Survey is a near-infrared photometric sky survey that covers nearly 1700 deg2towards the Galactic disc and bulge. It is well-suited to search for new open clusters, hidden behind dust and gas. The pipeline processed and calibrated KS -band tile images of 40 per cent of the disc area covered by VVVX was visually inspected for stellar overdensities. Then, we identified cluster candidates by examination of the composite JHKS colour images. The colour-magnitude diagrams of the cluster candidates are constructed. Whenever possible the Gaia DR2 parameters are used to calculate the mean proper motions, radial velocities, reddening and distances. We report the discovery of 120 new infrared clusters and stellar groups. Approximately half of them (47 per cent) are faint, compact, highly reddened, and they seem to be associated with other indicators of recent star formation, such as nearby Young Stellar Objects, Masers, H ii regions or bubbles. The preliminary distance determinations allow us to trace the clusters up to 4.5 kpc, but most of the cluster candidates are centred at 2.2 kpc. The mean proper motions of the clusters show that in general they follow the disc motion of the Galaxy. [ABSTRACT FROM AUTHOR]

A correction to the article "Infrared spectroscopy and analysis of brown dwarf and planetary mass objects in the Orion nebula cluster," published in a previous issue is presented.

Open clusters are key coeval structures that help us understand star formation, stellar evolution and trace the physical properties of our Galaxy. In the past years, the isolation of open clusters from the field has been heavily alleviated by the access to accurate large-scale stellar parallaxes and proper motions along a determined line of sight. Still, there are limitations regarding their completeness since large-scale studies rely on optical wavelengths. Here, we extend the open clusters sequences towards fainter magnitudes complementing the Gaia photometric and astrometric information with near-infrared data from the VVV survey. We performed a homogeneous analysis on 37 open clusters implementing two coarse-to-fine characterization methods: extreme deconvolution Gaussian mixture models coupled with an unsupervised machine learning method on eight-dimensional parameter space. The process allowed us to separate the clusters from the field at near-infrared wavelengths. We report an increase of ∼47 per cent new member candidates on average in our sample (considering only sources with high membership probability p  ≧ 0.9). This study is the second in a series intended to reveal open cluster near-infrared sequences homogeneously. [ABSTRACT FROM AUTHOR]

We present a study of the mid-infrared environments and association with star formation tracers of 6.7 GHz methanol masers taken from the Methanol Multi-Beam (MMB) survey. Our ultimate goal is to establish the mass of the host star and its evolutionary stage for each maser site. As a first step, the GLIMPSE survey of the Galactic plane is utilized to investigate the environment of 776 methanol masers and we find that while the majority of the masers are associated with mid-infrared counterparts, a significant fraction (17 per cent) are not associated with any detectable mid-infrared emission. A number of the maser counterparts are clearly extended with respect to the GLIMPSE point spread function and we implement an adaptive non-circular aperture photometry (ANCAP) technique to determine the fluxes of the maser counterparts. The ANCAP technique doubles the number of masers with flux information at all four wavelengths compared to the number of the corresponding counterparts obtained from the GLIMPSE Point Source Catalog. The colours of the maser counterparts are found to be very similar to the smaller study carried out by Ellingsen. The MMB masers are weakly associated with extended green objects and Red MSX Survey embedded sources (YSO and H ii region classifications) with 18 and 12 per cent of masers associated with these objects, respectively. The majority of MMB masers (60 per cent) have detectable GLIMPSE infrared counterparts but have not been identified with previously recognized tracers of massive star formation; this confirms that the MMB survey has the potential to identify massive star-forming regions independent of infrared selection. [ABSTRACT FROM PUBLISHER]

ABSTRACT We present a detailed study of a dust-obscured Galactic star cluster Mercer 5 ([MCM2005b] 5) in an extremely crowded field in the Milky Way. Near-infrared (near-IR) photometry from United Kingdom Infrared Digital Sky Surveys (UKIDSS) and the Son of ISAAC on the New Technology Telescope (SofI/NTT), combined with near-IR spectroscopy also from SofI, indicates that it is almost certainly a Galactic globular cluster, located at the edge of the Galactic bulge. The cluster suffers ∼9 mag of visual extinction, with strong evidence for an extinction gradient across the cluster. A simulation of the differential reddening in the cluster using empirical data from NGC 6539 (chosen because it had high signal-to-noise ratio data and low field star contamination) as a template mimics the observations extremely well. This simulation and other arguments are used to indicate that the most prominent clump of stars in the colour-magnitude diagrams is a horizontal branch clump. On this basis we conclude that the cluster is at a distance of ∼5.5 kpc and suffers from visual extinction ranging from ∼8.5 to ∼12.5 mag. Alternative explanations for its nature, such as a young cluster or an old open cluster, are much less likely, on the grounds of no visible main sequence or stars with IR excesses for the former and location versus lifetime arguments for the latter. [ABSTRACT FROM AUTHOR]

We report the discovery of 47 new T dwarfs in the Fourth Data Release (DR4) from the Large Area Survey (LAS) of the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey with spectral types ranging from T0 to T8.5. These bring the total sample of LAS T dwarfs to 80 as of DR4. In assigning spectral types to our objects we have identified eight new spectrally peculiar objects, and divide seven of them into two classes. H2O- H-early have a H2O- H index that differs with the H2O- J index by at least two subtypes. CH4- J-early have a CH4- J index that disagrees with the H2 index by at least two subtypes. We have ruled out binarity as a sole explanation for both types of peculiarity, and suggest that they may represent hitherto unrecognized tracers of composition and/or gravity. Clear trends in and are apparent for our sample, consistent with weakening absorption in the red wing of the K i line at 0.77 μm with decreasing effective temperature. We have used our sample to estimate space densities for T6–T9 dwarfs. By comparing our sample to Monte Carlo simulations of field T dwarfs for various mass functions of the form , we have placed weak constraints on the form of the field mass function. Our analysis suggests that the substellar mass function is declining at lower masses, with negative values of α preferred. This is at odds with results for young clusters that have been generally found to have . [ABSTRACT FROM AUTHOR]

We report the discovery of a very cool d/sdL7+T7.5p common proper motion binary system, SDSS J1416+13AB, found by cross-matching the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) Large Area Survey Data Release 5 (UKIDSS LAS DR4) against the Sloan Digital Sky Survey Data Release 7. The d/sdL7 is blue in and and has other features suggestive of low metallicity and/or high gravity. The T7.5p displays spectral peculiarity seen before in earlier type dwarfs discovered in UKIDSS LAS DR4, and referred to as CH4- J-early peculiarity, where the CH4- J index, based on the absorption to the red side of the J-band peak, suggests an earlier spectral type than the H2O- J index, based on the blue side of the J-band peak, by ∼2 subtypes. We suggest that CH4- J-early peculiarity arises from low metallicity and/or high gravity, and speculate as to its use for classifying T dwarfs. UKIDSS and follow-up United Kingdom Infrared Telescope/Wide Field CAMera (UKIRT/WFCAM) photometry shows the T dwarf to have the bluest near-infrared colours yet seen for such an object with . Warm Spitzer IRAC photometry shows the T dwarf to have extremely red , which is the reddest yet seen for a substellar object. The lack of parallax measurement for the pair limits our ability to estimate parameters for the system. However, applying a conservative distance estimate of 5–15 pc suggests a projected separation in range 45–135 au. By comparing colours of the T dwarf to spectral models, we estimate that and , with . This suggests a mass of ∼30 MJupiter for the T dwarf and an age of ∼10 Gyr for the system. The primary would then be a 75 MJupiter object with and a relatively dust-free atmosphere. Given the unusual properties of the system we caution that these estimates are uncertain. We eagerly await parallax measurements and high-resolution imaging which will constrain the parameters further. [ABSTRACT FROM AUTHOR]

In the past, it has generally been assumed that polarization observations made with ground-based telescopes are unaffected by the passage of light through the Earth's atmosphere. Here, we report observations with a new high-sensitivity astronomical polarimeter (PlanetPol) made during a Saharan dust event over the La Palma observatory in 2005 May that show excess linear polarization in the horizontal direction due to the passage of the starlight through the dust. The polarization reached a maximum value of at 56° zenith distance and varied over five nights in proportion to the change in dust optical depth. Polarization of transmitted light (dichroism) does not occur for spherical or randomly oriented non-spherical particles. Thus, these results imply that some fraction of the dust grain population aligns with a preferred orientation. We use T-matrix models to demonstrate that the observed polarization direction implies a vertical orientation for the long axis of the particles. We suggest a possible mechanism for vertical orientation resulting from the electric field in the atmosphere. These results will need to be taken into account in the design and use of future instruments for high-sensitivity astronomical polarimetry. The results also indicate possible new approaches to studying aerosol particles and their effects on the Earth's atmosphere. [ABSTRACT FROM AUTHOR]

The masses and temperatures of young low-mass stars and brown dwarfs in star-forming regions are not yet well established because of uncertainties in the age of individual objects and the spectral type–temperature scale appropriate for objects with ages of only a few Myr. Using multi-object optical spectroscopy, 45 low-mass stars and brown dwarfs in the Trapezium Cluster in Orion have been classified and 44 of these confirmed as bona fide cluster members. The spectral types obtained have been converted to effective temperatures using a temperature scale intermediate between those of dwarfs and giants, which is suitable for young pre-main-sequence objects. The objects have been placed on a Hertzsprung–Russell (HR) diagram overlaid with theoretical isochrones. The low-mass stars and the higher mass substellar objects are found to be clustered around the 1 Myr isochrone, while many of the lower mass substellar objects are located well above this isochrone. An average age of 1 Myr is found for the majority of the objects. Assuming coevality of the sources and an average age of 1 Myr, the masses of the objects have been estimated and range from . The spectra also allow an investigation of the surface gravity of the objects by measurement of the sodium doublet equivalent width. With one possible exception, all objects have low gravities, in line with young ages, and the Na indices for the Trapezium objects lie systematically below those of young stars and brown dwarfs in Chamaeleon, suggesting that the 820 nm Na index may provide a sensitive means of estimating ages in young clusters. [ABSTRACT FROM AUTHOR]

The spectral type is a key parameter in calibrating the temperature which is required to estimate the mass of young stars and brown dwarfs. We describe an approach developed to classify low-mass stars and brown dwarfs in the Trapezium Cluster using red optical spectra, which can be applied to other star-forming regions. The classification uses two methods for greater accuracy: the use of narrow-band spectral indices which rely on the variation of the strength of molecular lines with spectral type and a comparison with other previously classified young, low-mass objects in the Chamaeleon I star-forming region. We have investigated and compared many different molecular indices and have identified a small number of indices which work well for classifying M-type objects in nebular regions. The indices are calibrated for young, pre-main-sequence objects whose spectra are affected by their lower surface gravities compared with those on the main sequence. Spectral types obtained are essentially independent of both reddening and nebular emission lines. Confirmation of candidate young stars and brown dwarfs as bona fide cluster members may be accomplished with moderate resolution spectra in the optical region by an analysis of the strength of the gravity-sensitive Na doublet. It has been established that this feature is much weaker in these very young objects than in field dwarfs. A sodium spectral index is used to estimate the surface gravity and to demonstrate quantitatively the difference between young (1–2 Myr) objects, and dwarf and giant field stars. [ABSTRACT FROM AUTHOR]

Using a simulated disc brown dwarf (BD) population, we find that new large area infrared surveys are expected to identify enough BDs covering wide enough mass–age ranges to potentially measure the present day mass function down to , and the BD formation history out to 10 Gyr, at a level that will be capable of establishing if BD formation follows star formation. We suggest these capabilities are best realized by spectroscopic calibration of BD properties ( and [M/H]) which when combined with a measured luminosity and an evolutionary model can give BD mass and age relatively independent of BD atmosphere models. Such calibration requires an empirical understanding of how BD spectra are affected by variations in these properties, and thus the identification and study of ‘benchmark BDs’ whose age and composition can be established independently. We identify the best sources of benchmark BDs as young open cluster members, moving group members, and wide (>1000 au) BD companions to both subgiant stars and high-mass white dwarfs (WDs). To accurately asses the likely number of wide companion BDs available, we have constrained the wide L dwarf companion fraction using the 2-Micron All Sky Survey (2MASS), and find a companion fraction of for separations of ∼1000–5000 au. This equates to a BD companion fraction of if one assumes an companion mass function. Using this BD companion fraction, we simulate populations of wide BD binaries, and estimate that subgiant–BD binaries, and benchmark WD–BD binaries could be identified using current and new facilities. The WD–BD binaries should all be identifiable using the Large Area Survey component of the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey, combined with the Sloan Digital Sky Survey. Discovery of the subgiant–BD binaries will require a near-infrared imaging campaign around a large (∼900) sample of Hipparcos subgiants. If identified, spectral studies of these benchmark BD populations could reveal the spectral sensitivities across the and [M/H] space probed by new surveys. [ABSTRACT FROM AUTHOR]