344 research outputs found
Astrometric and photometric initial mass functions from the UKIDSS Galactic Clusters Survey - II. The Alpha Persei open cluster
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2012 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We present the results of a deep (J = 19.1mag) infrared (ZYJHK) survey over the full α Per open cluster extracted from the Data Release 9 of the United Kingdom Infrared Telescope Infrared Deep Sky Survey Galactic Clusters Survey (UKIDSS). We have selected ∼700 cluster member candidates in ∼56 square degrees in α Per by combining photometry in five near-infrared passbands and proper motions derived from the multiple epochs provided by the UKIDSS Galactic Clusters Survey (GCS) Data Release 9 (DR9). We also provide revised membership for all previously published α Per low-mass stars and brown dwarfs recovered in GCS based on the new photometry and astrometry provided by DR9. We find no evidence of K-band variability in members of α Per with dispersion less than 0.06-0.09mag. We employed two independent but complementary methods to derive the cluster luminosity and mass functions: a probabilistic analysis and a more standard approach consisting of stricter astrometric and photometric cuts. We find that the resulting luminosity and mass functions obtained from both methods are consistent. We find that the shape of the α Per mass function is similar to that of the Pleiades although the characteristic mass may be higher after including higher mass data from earlier studies (the dispersion is comparable). We conclude that the mass functions of α Per, the Pleiades and Praesepe are best reproduced by a log-normal representation similar to the system field mass function although with some variation in the characteristic mass and dispersion values.Peer reviewe
Spectroscopy of Hyades L dwarf candidates
We present the results of photometric, astrometric, and spectroscopic
follow-up of L dwarf candidates identified in the Hyades cluster by Hogan et
al. (2008). We obtained low-resolution optical spectroscopy with the OSIRIS
spectrograph on the Gran Telescopio de Canarias for all 12 L dwarf candidates
as well as new J-band imaging for a subsample of eight to confirm their proper
motion. We also present mid-infrared photometry from the Wise Field Infrared
Survey Explorer (WISE) for the Hyades L and T dwarf candidates and estimate
their spectroscopic distances, effective temperatures, and masses. We confirm
the cool nature of several L dwarf candidates and confirm astrometrically their
membership, bridging the gap between the coolest M dwarfs and the two T dwarfs
previously reported in the Hyades cluster. These members represent valuable
spectral templates at an age of 625 Myr and slightly super solar metallicity
(Fe/H=+0.13). We update the Hyades mass function across the hydrogen-burning
limit and in the substellar regime. We confirm a small number numbers of
very-low-mass members below ~0.1 Msun belonging to the Hyades cluster.Comment: 12 pages, 7 figures, 3 tables; accepted for publication in MNRA
Magneto-optical Kerr effect in Weyl semimetals with broken inversion and time-reversal symmetries
The topological nature of the band structure of a Weyl semimetal leads to a
number of unique transport and optical properties. For example, the description
of the propagation of an electromagnetic wave in a Weyl semimetal with broken
time-reversal and inversion symmetry, for example, requires a modification of
the Maxwell equations by the axion field where is the separation
in wave vector space between two Weyl nodes of opposite chiralities and
is their separation in energy. In this paper, we study
theoretically how the axion terms and modify the frequency
behavior of the Kerr rotation and ellipticity angles and in a Weyl semimetal. Both the
Faraday and Voigt configurations are considered since they provide different
information on the electronic transitions and plasmon excitation. We derive the
Kerr angles firstly without an external magnetic field where the rotation of
the polarization is only due to the axion terms and secondly in a strong
magnetic field where these terms compete with the gyration effect of the
magnetic field. In this latter case, we concentrate on the ultra-quantum limit
where the Fermi level lies in the chiral Landau level and the Kerr and
ellipticity angles have more complex frequency and magnetic field behaviors.Comment: 21 pages with 14 PDF figure
Calcium-dependent release of adenosine and uridine nucleotides from A549 cells
Extracellular nucleotides play an important role in lung defense, but the release mechanism and relative abundance of different nucleotide species secreted by lung epithelia are not well defined. In this study, to minimize cell surface hydrolysis, we used a low-volume, flow-through chamber and examined adenosine and uridine nucleotide concentrations in perfusate aliquots of human lung A549 cells challenged by 50% hypotonic shock. Adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), and adenosine (Ado) were quantified in high-performance liquid chromatography (HPLC) analysis of fluorescent etheno derivatives, and uridine triphosphate (UTP) and uridine diphosphate (UDP) were measured using HPLC-coupled radioenzymatic assays. After the onset of hypotonic shock, ATP, ADP, UTP, and UDP in the perfusates increased markedly and peaked at approximately 2.5 min, followed by a gradual decay in the next 15–20 min; peak changes in Ado and AMP were relatively minor. The peak concentrations and fold increment (in parentheses) were: 34 ± 13 nM ATP (5.6), 11 ± 5 nM ADP (3.7), 3.3 ± 1.2 nM AMP (1.4), 23 ± 7 nM Ado (2.1), 21 nM UTP (>7), and 11 nM UDP (27). Nucleotide release was almost completely abolished from cells loaded with the calcium chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA). Under isotonic conditions, elevation of intracellular calcium with the calcium ionophore ionomycin (5 μM, 3 min) also released nucleotides with kinetics and relative abundance as above, albeit less robust. ADP:ATP (1:3) and UDP:UTP (1:2) ratios in perfusates from stimulated cells were markedly higher than the cytosolic ratios of these species, suggesting that a nucleotide diphosphate (NDP)-rich compartment, e.g., the secretory pathway, contributed to nucleotide release. Laser confocal microscopy experiments illustrated increased FM1-43 uptake into the plasma membrane upon hypotonic shock or ionomycin treatment, consistent with enhanced vesicular exocytosis under these conditions. In summary, our results strongly suggest that calcium-dependent exocytosis is responsible, at least in most part, for adenosine and uridine nucleotide release from A549 cells
Low Mass Stars and Brown Dwarfs in Praesepe
Presented are the results of a large and deep optical-near-infrared
multi-epoch survey of the Praesepe open star cluster using data from the UKIDSS
Galactic Clusters Survey. Multiple colour magnitude diagrams were used to
select potential members and proper motions were used to assign levels of
membership probability. From our sample, 145 objects were designated as high
probability members (p >= 0.6) with most of these having been found by previous
surveys although 14 new cluster members are also identified. Our membership
assignment is restricted to the bright sample of objects (Z < 18). From the
fainter sample, 39 candidates were found from an examination of multiple colour
magnitude plots. Of these, 2 have small but significant membership
probabilities. Finally, using theoretical models, cluster luminosity and mass
functions were plotted with the later being fitted with a power law of alpha =
1.11 +/- 0.37 for the mass range 0.6 to 0.125 Msun and an assumed cluster age
of 500 Myrs in the UKIDSS Z photometric band. Likewise taking an assumed
cluster age of 1 Gyr we find alpha = 1.10 +/- 0.37. Similar values were also
found for the J and K bands. These results compare favourably with the result
of Kraus & Hillenbrand (2007) (alpha = 1.4 +/- 0.2) but are significantly lower
than that of the more recent study conducted by Boudreault et al. (2009) (alpha
= 1.8 +/- 0.1).Comment: 21 pages, 11 figures, 3 tables and 4 appendices. Accepted for
publication in MNRAS, corrected a missing referenc
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