scholarly journals Trigonometric parallaxes of young field L dwarfs

2014 ◽  
Vol 568 ◽  
pp. A6 ◽  
Author(s):  
M. R. Zapatero Osorio ◽  
V. J. S. Béjar ◽  
P. A. Miles-Páez ◽  
K. Peña Ramírez ◽  
R. Rebolo ◽  
...  
Keyword(s):  
Trigonometric Parallaxes ◽  
Field L ◽  
L Dwarfs

scholarly journals A Sample of Very Young Field L Dwarfs and Implications for the Brown Dwarf “Lithium Test” at Early Ages

2008 ◽  
Vol 689 (2) ◽  
pp. 1295-1326 ◽  
Author(s):  
J. Davy Kirkpatrick ◽  
Kelle L. Cruz ◽  
Travis S. Barman ◽  
Adam J. Burgasser ◽  
Dagny L. Looper ◽  
...  
Keyword(s):  
Brown Dwarf ◽  
Field L ◽  
L Dwarfs

scholarly journals Parallaxes of Brown Dwarfs at USNO

2003 ◽  
Vol 211 ◽  
pp. 409-412
Author(s):  
Hugh C. Harris ◽  
Conard C. Dahn ◽  
Frederick J. Vrba ◽  
Harry H. Guetter ◽  
Blaise Canzian ◽  
...  
Keyword(s):  
Spectral Type ◽  
Tangential Velocity ◽  
Brown Dwarfs ◽  
Absolute Magnitude ◽  
Rotation Velocity ◽  
Measurable Parameter ◽  
Trigonometric Parallaxes ◽  
Hα Emission ◽  
L Dwarfs ◽  
Absolute Magnitudes

Trigonometric parallaxes have been measured by Dahn et al. (2002) for 28 cool dwarfs and brown dwarfs, including 17 L dwarfs and three T dwarfs. Broadband CCD and near-IR photometry (VRIz*JHK) have been obtained for these objects and for 24 additional late-type dwarfs. These data have been supplemented with astrometry and photometry from the literature, including parallaxes for the brighter companions of ten L and two T dwarfs. The absolute magnitudes and colors are reviewed here. The I - J color and the spectral type are both good predictors of absolute magnitude for late-M and L dwarfs. MJ becomes monotonically fainter with I - J color and with spectral type through late-L dwarfs, then brightens for early-T dwarfs. In contrast, the J - K color correlates poorly with absolute magnitude for L dwarfs. Using several other parameters from the literature (Li detection, Hα emission strength, projected rotation velocity, and tangential velocity), we fail to uncover any measurable parameter that correlates with the anomalous J - K color.

scholarly journals A Focus on L Dwarfs with Trigonometric Parallaxes

2018 ◽  
Vol 130 (988) ◽  
pp. 064402 ◽  
Author(s):  
Y. Wang ◽  
R. L. Smart ◽  
Z. Shao ◽  
H. R. A Jones ◽  
F. Marocco ◽  
...  
Keyword(s):  
Trigonometric Parallaxes ◽  
L Dwarfs

Statistics and parallaxes

1978 ◽  
Vol 48 ◽  
pp. 7-29
Author(s):  
T. E. Lutz
Keyword(s):  
Experimental Design ◽  
Statistical Methods ◽  
Review Paper ◽  
Systematic Errors ◽  
Past Experience ◽  
Random Errors ◽  
Trigonometric Parallaxes ◽  
Systematic And Random Errors

This review paper deals with the use of statistical methods to evaluate systematic and random errors associated with trigonometric parallaxes. First, systematic errors which arise when using trigonometric parallaxes to calibrate luminosity systems are discussed. Next, determination of the external errors of parallax measurement are reviewed. Observatory corrections are discussed. Schilt’s point, that as the causes of these systematic differences between observatories are not known the computed corrections can not be applied appropriately, is emphasized. However, modern parallax work is sufficiently accurate that it is necessary to determine observatory corrections if full use is to be made of the potential precision of the data. To this end, it is suggested that a prior experimental design is required. Past experience has shown that accidental overlap of observing programs will not suffice to determine observatory corrections which are meaningful.

scholarly journals Variability of L Dwarfs in the Near Infrared

2003 ◽  
Vol 211 ◽  
pp. 455-456 ◽  
Author(s):  
José A. Caballero ◽  
Víctor J. S. Béjar ◽  
Rafael Rebolo
Keyword(s):  
Time Scales ◽  
Near Infrared ◽  
Brown Dwarfs ◽  
L Dwarfs ◽  
Atmospheric Changes ◽  
Changes Over Time ◽  
Over Time

We have obtained series of images in the near infrared J and Ks bands for seven L-type dwarfs with a duration of 3 to 6 hours. We present results on: 1) the amplitude of variability associated with atmospheric changes over time scales from minutes to several hours; 2) the search for cool companions in wide orbits; 3) the search for transits of brown dwarfs and planetary companions in very close orbits.

scholarly journals Luminosity of δ Scuti Stars After Hipparcos Satellite

1998 ◽  
Vol 11 (1) ◽  
pp. 567-567
Author(s):  
E. Antonello ◽  
L. Mantegazza ◽  
E. Poretti
Keyword(s):  
Globular Clusters ◽  
Rotational Velocity ◽  
High Amplitude ◽  
Empirical Dependence ◽  
Trigonometric Parallaxes ◽  
Nearby Stars ◽  
Observational Errors ◽  
Absolute Magnitudes ◽  
Scuti Stars ◽  
Δ Scuti Stars

The absolute magnitudes of δ Scuti stars derived from parallaxes measured by the Hipparcos satellite were compared with the previous estimates based on photometric uvby² indices, and significant differences were found which are related to photometric effects of metallicity and rotational velocity. A reliable calibration of Mv in terms of the photometric indices shall include an estimate of these effects. It is important also to take into account the possible presence of unresolved close companions in order to fully exploit the accuracy of Mv of nearby stars derived from the trigonometric parallaxes. The Mv of few bright SX Phe stars support the period-luminosity relation obtained with ground based observations of globular clusters, while it does not seem to confirm the empirical dependence of this relation on the metallicity. Some high amplitude δ Scuti stars with intermediate or normal metallicity and small and uncertain parallax have apparently a very low luminosity. Simulations of Mv determinations from observed parallaxes based on the discussion of observational errors by Lutz and Kelker (1973) have shown that the low luminosity could be an effect related to these errors.

scholarly journals A Biologically Plausible Computational Model for Auditory Object Recognition

2009 ◽  
Vol 101 (1) ◽  
pp. 323-331 ◽  
Author(s):  
Eric Larson ◽  
Cyrus P. Billimoria ◽  
Kamal Sen
Keyword(s):  
Object Recognition ◽  
Spike Train ◽  
Nearest Neighbor ◽  
Primary Auditory Cortex ◽  
Spike Trains ◽  
Coincidence Detection ◽  
Model Based ◽  
Plausible Model ◽  
Field L ◽  
Song Discrimination

Object recognition is a task of fundamental importance for sensory systems. Although this problem has been intensively investigated in the visual system, relatively little is known about the recognition of complex auditory objects. Recent work has shown that spike trains from individual sensory neurons can be used to discriminate between and recognize stimuli. Multiple groups have developed spike similarity or dissimilarity metrics to quantify the differences between spike trains. Using a nearest-neighbor approach the spike similarity metrics can be used to classify the stimuli into groups used to evoke the spike trains. The nearest prototype spike train to the tested spike train can then be used to identify the stimulus. However, how biological circuits might perform such computations remains unclear. Elucidating this question would facilitate the experimental search for such circuits in biological systems, as well as the design of artificial circuits that can perform such computations. Here we present a biologically plausible model for discrimination inspired by a spike distance metric using a network of integrate-and-fire model neurons coupled to a decision network. We then apply this model to the birdsong system in the context of song discrimination and recognition. We show that the model circuit is effective at recognizing individual songs, based on experimental input data from field L, the avian primary auditory cortex analog. We also compare the performance and robustness of this model to two alternative models of song discrimination: a model based on coincidence detection and a model based on firing rate.

scholarly journals Role of the Zebra Finch Auditory Thalamus in Generating Complex Representations for Natural Sounds

2010 ◽  
Vol 104 (2) ◽  
pp. 784-798 ◽  
Author(s):  
Noopur Amin ◽  
Patrick Gill ◽  
Frédéric E. Theunissen
Keyword(s):  
Receptive Fields ◽  
Neural Representation ◽  
Natural Sounds ◽  
Auditory Midbrain ◽  
Complex Sounds ◽  
Auditory Thalamus ◽  
Spectrotemporal Receptive Fields ◽  
Primary Sensory Cortex ◽  
Relay Nucleus ◽  
Field L

We estimated the spectrotemporal receptive fields of neurons in the songbird auditory thalamus, nucleus ovoidalis, and compared the neural representation of complex sounds in the auditory thalamus to those found in the upstream auditory midbrain nucleus, mesencephalicus lateralis dorsalis (MLd), and the downstream auditory pallial region, field L. Our data refute the idea that the primary sensory thalamus acts as a simple, relay nucleus: we find that the auditory thalamic receptive fields obtained in response to song are more complex than the ones found in the midbrain. Moreover, we find that linear tuning diversity and complexity in ovoidalis (Ov) are closer to those found in field L than in MLd. We also find prevalent tuning to intermediate spectral and temporal modulations, a feature that is unique to Ov. Thus even a feed-forward model of the sensory processing chain, where neural responses in the sensory thalamus reveals intermediate response properties between those in the sensory periphery and those in the primary sensory cortex, is inadequate in describing the tuning found in Ov. Based on these results, we believe that the auditory thalamic circuitry plays an important role in generating novel complex representations for specific features found in natural sounds.

scholarly journals The Luminosity Determination

1995 ◽  
Vol 10 ◽  
pp. 399-402
Author(s):  
A.E. Gómez ◽  
C. Turon
Keyword(s):  
Main Sequence ◽  
Small Volume ◽  
Absolute Magnitude ◽  
Fitting Procedure ◽  
Trigonometric Parallaxes ◽  
The Mean ◽  
The Absolute ◽  
Absolute Magnitudes ◽  
Kinematical Data ◽  
Magnitude Determination

The Hertzprung-Russel (HR) diagram luminosity calibration relies basically on three kinds of data: trigonometric parallaxes, kinematical data (proper motions and radial velocities) and cluster distances obtained by the zero-age main sequence fitting procedure. The most fundamental method to calculate the absolute magnitude is the use of trigonometric parallaxes, but up to now, accurate data only exist for stars contained in a small volume around the sun. Individual absolute magnitudes are obtained using trigonometric parallaxes or photometric and spectroscopic calibrations. In these calibrations the accuracy on the absolute magnitude determination ranges from ±0.m2 in the main sequence to ±0m5 in the giant branch. On the other hand, trigonometric parallaxes, kinematical data or cluster distances have been used to make statistical calibrations of the absolute magnitude. The standard error on the mean absolute magnitude calibrations ranges from ±0m3 to ±0m6 on the mean sequence, from ±0m5 to ±0m7 on thegiant branch and is of about 1mfor supergiants.Future improvements in the absolute magnitude determination will depend on the improvement of the basic data from the ground and space. A brief overview of the new available data is presented. In particular, the analysis of the first 30 months data of the Hipparcos mission (H30) (from the 37 months data of the whole mission) allows to perform a statistical evaluation of the improvements expected in the luminosity determination.

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