The discovery and subsequent detailed study of T dwarfs have provided many surprises and pushed the physics and modelling of cool atmospheres in unpredicted directions. Distance is a critical ...parameter for studies of these objects to determine intrinsic luminosities, test binarity and measure their motion in the Galaxy. We describe a new observational programme to determine distances across the full range of T-dwarf subtypes using the New Technology Telescope (NTT)/SOFI telescope/instrument combination. We present preliminary results for ten objects, five of which represent new distances.
To improve precision management and the cost effectiveness of forest practices, we investigate a pre-harvest airborne laser scanning (ALS) forest inventory with an unmanned aerial vehicle (UAV) ...acquired post-harvest digital aerial photogrammetry (DAP) inventory to identify the location and residual volume of stands following selection harvesting. ALS data and field measurements collected pre-harvest in 2013 (T
1
) and UAV imagery collected post-harvest in 2015 (T
2
) were processed to produce analogous point clouds of the study area near Williams Lake, British Columbia, Canada. Tree height, diameter at breast height (DBH), and species were recorded from systematically located variable radius plots subsequent to ALS and DAP collection. Point cloud metrics and field measurements from each data set were used to create T
1
ALS and T
2
DAP predictive volume models. Direct and indirect volume change estimates were created from the difference between T
1
ALS and T
2
DAP model results. The estimated root mean square error (RMSE) for volume was 17.34% and 18.50% for the 2013 ALS and 2015 DAP models, respectively. The indirect and direct models predicting volume change produced errors of 16.65% and 86.56%, respectively. Results achieved from ALS and DAP models indicate strong potential for inventories generated using UAV-acquired DAP to estimate the quantity and location of residual volume after harvest operations, and could be applied in tandem to act as a semi-automated inventory cycling method to improve operational efficiency and cost effectiveness in Canadian forest management.
Aims. In this work we present chromospheric activity indices, kinematics, radial-velocities, and rotational velocities for more than 850 FGK-type dwarfs and subgiant stars in the southern hemisphere ...and test how best to calibrate and measure S-indices from echelle spectra. Methods. We measured our parameters using the high-resolution and high-S/N FEROS echelle spectra acquired for this purpose. Results. We confirm the bimodal distribution of chromospheric activities for such stars and highlight the role that the more active K-dwarfs play in biasing the number of active stars. We show that the age-activity relationship does appear to continue to ages older than the Sun if we simply compare main sequence stars and subgiant stars with an offset of around 2.5 Gyr between the peaks of both distributions. Also we show evidence of an increased spin-down timescale for cool K dwarfs compared with earlier F and G type stars. We highlight that activities drawn from low-resolution spectra (R < 2500) significantly increase the rms scatter when calibrating onto common systems of measurements like the Mt. Wilson system. Also we show that older and widely used catalogues of activities in the south appear to be offset compared to more recent works at the ~0.1 dex level in \hbox{$\log R'_{\rm{HK}}$}logRHK′ through calibrator drift. In addition, we show how kinematics can be used to preselect inactive stars for future planet search projects. We see the well known trend between projected rotational velocity and activity, however we also find a correlation between kinematic space velocity and chromospheric activity. It appears that after the Vaughan-Preston gap there is a quick step function in the kinematic space motion towards a significantly broader spread in velocities. We speculate on reasons for this correlation and provide some model scenarios to describe the bimodal activity distribution through magnetic saturation, residual low level gas accretion, or accretion by the star of planets or planetesimals. Finally, we provide a new empirical measurement for the disk-heating law, using the latest age-activity relationships to reconstruct the age-velocity distribution for local disk stars. We find a value of 0.337 ± 0.045 for the exponent of this power law (i.e. σtot ∝ t0.337), in excellent agreement with those found using isochrone fitting methods and with theoretical disk-heating models.
We report the discovery of three very late T dwarfs in the UKIRT Infrared Deep Sky Survey (UKIDSS) Third Data Release: ULAS J101721.40+011817.9 (ULAS1017), ULAS J123828.51+095351.3 (ULAS1238) and ...ULAS J133553.45+113005.2 (ULAS1335). We detail optical and near-infrared (NIR) photometry for all three sources, and mid-IR photometry for ULAS1335. We use NIR spectra of each source to assign spectral types T8p (ULAS1017), T8.5 (ULAS1238) and T9 (ULAS1335) to these objects. ULAS1017 is classed as a peculiar T8 (T8p) due to appearing as a T8 dwarf in the J band, whilst exhibiting H- and K-band flux ratios consistent with a T6 classification. Through comparison to BT-Settl model spectra we estimate that ULAS1017 has 750 K ≲Teff≲ 850 K, and 5.0 ≲ log g(cm s−2) ≲ 5.5, assuming solar metallicity. This estimate for gravity is degenerate with varying metallicity. We estimate that ULAS1017 has an age of 1.6–15 Gyr, a mass of 33–70MJ and lies at a distance of 31–54 pc. We do not estimate atmospheric parameters for ULAS1238 due to a lack of K-band photometry. We extend the unified scheme of Burgasser et al. to the type T9 and suggest the inclusion of the WJ index to replace the now saturated J-band indices. We propose ULAS1335 as the T9 spectral type standard. ULAS1335 is the same spectral type as ULAS J003402.77−005206.7 and CFBDS J005910.90−011401.3. We argue that given the similarity of the currently known >T8 dwarfs to the rest of the T dwarf sequence, the suggestion of the Y0 spectral class for these objects is premature. Comparison of model spectra with that of ULAS1335 suggest a temperature below 600 K, possibly combined with low gravity and/or high metallicity. We find ULAS1335 to be extremely red in NIR to mid-IR colours, with H−4.49= 4.34 ± 0.04. This is the reddest NIR to mid-IR colour yet observed for a T dwarf. The NIR to mid-IR spectral energy distribution of ULAS1335 further supports Teff < 600 K, and we estimate Teff∼ 550–600 K for ULAS1335. We estimate that ULAS1335 has an age of 0.6–5.3 Gyr, a mass of 15–31MJ and lies at a distance of 8–12 pc.
Although HIV/AIDS has been anything but neglected over the last decade, opportunistic infections (OIs) are increasingly overlooked as large-scale donors shift their focus from acute care to ...prevention and earlier antiretroviral treatment (ART) initiation. Of these OIs, cryptococcal meningitis, a deadly invasive fungal infection, continues to affect hundreds of thousands of HIV patients with advanced disease each year and is responsible for an estimated 15%–20% of all AIDS-related deaths 1, 2. Yet cryptococcal meningitis ranks amongst the most poorly funded “neglected” diseases in the world, receiving 0.2% of available relevant research and development (R&D) funding, according to Policy Cures’ 2016 Global Funding of Innovation for Neglected Diseases (G-Finder) Report 3, 4.
The discovery of a very cool binary system Burningham, Ben; Leggett, S. K.; Lucas, P. W. ...
Monthly notices of the Royal Astronomical Society,
June 2010, Volume:
404, Issue:
4
Journal Article
Peer reviewed
Open access
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 J−H and H−K 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 H−K=−1.31 ± 0.17. Warm Spitzer IRAC photometry shows the T dwarf to have extremely red H−4.5= 4.86 ± 0.04, 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 H−K:H−4.5 colours of the T dwarf to spectral models, we estimate that Teff= 500 K and M/H∼− 0.30, with log g∼ 5.0. 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 log g∼ 5.5 and a relatively dust-free Teff∼ 1500 K 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.
The properties of the T8.5p dwarf Ross 458C Burningham, Ben; Leggett, S. K.; Homeier, D. ...
Monthly notices of the Royal Astronomical Society,
07/2011, Volume:
414, Issue:
4
Journal Article
Peer reviewed
Open access
We present near-infrared photometry and spectroscopy, and warm-Spitzer IRAC photometry of the young very cool T dwarf Ross 458C, which we have typed as T8.5p. By applying the fiducial age constraints ...(≤1 Gyr) imposed by the properties of the active M dwarf Ross 458A, we have used these data to determine that Ross 458C has T
eff= 695 ± 60 K, log g= 4.0-4.7 and an inferred mass of 5-20M
J. We have compared fits of the near-infrared spectrum and IRAC photometry to the BT Settl and Saumon & Marley model grids, and have found that both sets provide best fits that are consistent with our derived properties, whilst the former provide a marginally closer match to the data for all scenarios explored here. The main difference between the model grids arises in the 4.5-μm region, where the BT Settl models are able to better predict the flux through the IRAC filter, suggesting that non-equilibrium effects on the CO-CO2 ratio are important for shaping the mid-infrared spectra of very cool T dwarfs. We have also revisited the issue of the dust opacity in the spectra of Ross 458C that was raised by Burgasser et al. We have found that the BT Settl models which also incorporate a condensate cloud model provide a better match to the near-infrared spectrum of this target than the Saumon & Marley model with f
sed= 2 and we briefly discuss the influence of condensate clouds on T dwarf spectra.
Red subdwarfs in binary systems are crucial for both model calibration and spectral classification. We search for red subdwarfs in binary systems from a sample of high proper motion objects with ...Sloan Digital Sky Survey spectroscopy. We present here discoveries from this search, as well as highlight several additional objects of interest. We find 30 red subdwarfs in wide binary systems including: two with spectral type of esdM5.5, 6 companions to white dwarfs and 3 carbon-enhanced red subdwarfs with normal red subdwarf companions. 15 red subdwarfs in our sample are partially resolved close binary systems. With this binary sample, we estimate the low limit of the red subdwarf binary fraction of ∼10 per cent. We find that the binary fraction goes down with decreasing masses and metallicities of red subdwarfs. A spectroscopic esdK7 subdwarf + white dwarf binary candidate is also reported. 30 new M subdwarfs have spectral type of ≥M6 in our sample. We also derive relationships between spectral types and absolute magnitudes in the optical and near-infrared for M and L subdwarfs, and we present an M subdwarf sample with measured U, V, W space velocities.
We present i and z photometry for 25 T dwarfs and 1 L dwarf. Combined with published photometry, the data show that the i - z, z - Y, and z - J colors of T dwarfs are very red, and continue to ...increase through to the late-type T dwarfs, with a hint of a saturation for the latest types with T sub(eff) approx =600 K. We present new 0.7-1.0 mu m and 2.8-4.2 mu m spectra for the very late type T dwarf UGPS J072227.51-054031.2, as well as improved astrometry for this dwarf. Examination of the spectral energy distribution using new and published data, with Saumon & Marley models, shows that the dwarf has T sub(eff) = 505 + or - 10 K, a mass of 3-11 M sub(Jupiter), and an age between 60 Myr and 1 Gyr. This young age is consistent with the thin disk kinematics of the dwarf. The mass range overlaps with that usually considered to be planetary, despite this being an unbound object discovered in the field near the Sun. This apparently young rapid rotator is also undergoing vigorous atmospheric mixing, as determined by the IRAC and WISE 4.5 mu m photometry and the Saumon & Marley models. The optical spectrum for this 500 K object shows clearly detected lines of the neutral alkalis Cs and Rb, which are emitted from deep atmospheric layers with temperatures of 900-1200 K.
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