8,437 research outputs found
Procedimiento Estimación Incertidumbre En Un Sistema De Medida Caso Magnetómetro Hall
En este trabajo se presenta un método para estimar el valor de incertidumbre asociada a la medida por un sistema de medición electrónico, como componente metrológico en el proceso de diseño y construcción de un sistema de medida genérico. En este caso especifico, para un magnetómetro Hall de precisión. El método usado es por comparación con un equipo patrón. También se determina el error en la medida aportado por los diferentes componentes del sistema de acondicionamiento en el sistema de medida. El procedimiento plantea un valor para la incertidumbre en la medida de campo magnético de 0.8 % y un error de 0.2 %. El error es aportado por los diferentes componentes del sistema de instrumentación
Procedimiento Estimación Incertidumbre En Un Sistema De Medida Caso Magnetómetro Hall
En este trabajo se presenta un método para estimar el valor de incertidumbre asociada a la medida por un sistema de medición electrónico, como componente metrológico en el proceso de diseño y construcción de un sistema de medida genérico. En este caso especifico, para un magnetómetro Hall de precisión. El método usado es por comparación con un equipo patrón. También se determina el error en la medida aportado por los diferentes componentes del sistema de acondicionamiento en el sistema de medida. El procedimiento plantea un valor para la incertidumbre en la medida de campo magnético de 0.8 % y un error de 0.2 %. El error es aportado por los diferentes componentes del sistema de instrumentación
HAT-P-12b: A Low-Density Sub-Saturn Mass Planet Transiting a Metal-Poor K Dwarf
We report on the discovery of HAT-P-12b, a transiting extrasolar planet
orbiting the moderately bright V=12.8 K4 dwarf GSC 03033-00706, with a period P
= 3.2130598 +- 0.0000021 d, transit epoch Tc = 2454419.19556 +- 0.00020 (BJD)
and transit duration 0.0974 +- 0.0006 d. The host star has a mass of 0.73 +-
0.02 Msun, radius of 0.70 +- ^0.02_0.01 Rsun, effective temperature 4650 +- 60
K and metallicity [Fe/H] = -0.29 +- 0.05. We find a slight correlation between
the observed spectral line bisector spans and the radial velocity, so we
consider, and rule out, various blend configurations including a blend with a
background eclipsing binary, and hierarchical triple systems where the
eclipsing body is a star or a planet. We conclude that a model consisting of a
single star with a transiting planet best fits the observations, and show that
a likely explanation for the apparent correlation is contamination from
scattered moonlight. Based on this model, the planetary companion has a mass of
0.211 +- 0.012 MJup, and a radius of 0.959 +- ^0.029_0.021 RJup yielding a mean
density of 0.295 +- 0.025 g cm^-3. Comparing these observations with recent
theoretical models we find that HAT-P-12b is consistent with a ~ 1-4.5 Gyr,
mildly irradiated, H/He dominated planet with a core mass Mc <~ 10 Mearth.
HAT-P-12b is thus the least massive H/He dominated gas giant planet found to
date. This record was previously held by Saturn.Comment: Accepted for publication in ApJ, 13 pages, 9 figures, 5 table
HAT-P-15b: A 10.9-day Extrasolar Planet Transiting a Solar-type Star
We report the discovery of HAT-P-15b, a transiting extrasolar planet in the
`period valley', a relatively sparsely-populated period regime of the known
extrasolar planets. The host star, GSC 2883-01687, is a G5 dwarf with V=12.16.
It has a mass of 1.01+/-0.04 M(Sun), radius of 1.08+/-0.04 R(Sun), effective
temperature 5568+/-90 K, and metallicity [Fe/H] = +0.22+/-0.08. The planetary
companion orbits the star with a period 10.863502+/-0.000027 days, transit
epoch Tc = 2454638.56019+/-0.00048 (BJD), and transit duration 0.2285+/-0.0015
days. It has a mass of 1.946+/-0.066 M(Jup), and radius of 1.072+/-0.043 R(Jup)
yielding a mean density of 1.96+/-0.22 g/cm3. At an age of 6.8+/-2.1 Gyr, the
planet is H/He-dominated and theoretical models require about 2% (10 M(Earth))
worth of heavy elements to reproduce its measured radius. With an estimated
equilibrium temperature of 820 K during transit, and 1000 K at occultation,
HAT-P-15b is a potential candidate to study moderately cool planetary
atmospheres by transmission and occultation spectroscopy.Comment: 12 pages with 10 figures and 6 tables in emulateapj format. Submitted
to The Astrophysical Journa
Cyclin-Dependent Kinase Inhibitor p21 Controls Adult Neural Stem Cell Expansion by Regulating Sox2 Gene Expression
In the adult brain, continual neurogenesis of olfactory neurons is sustained by the existence of neural stem cells (NSCs) in the subependymal niche. Elimination of the cyclin-dependent kinase inhibitor 1A (p21) leads to premature exhaustion of the subependymal NSC pool, suggesting a relationship between cell cycle control and long-term self-renewal, but the molecular mechanisms underlying NSC maintenance by p21 remain unexplored. Here we identify a function of p21 in the direct regulation of the expression of pluripotency factor Sox2, a key regulator of the specification and maintenance of neural progenitors. We observe that p21 directly binds a Sox2 enhancer and negatively regulates Sox2 expression in NSCs. Augmented levels of Sox2 in p21 null cells induce replicative stress and a DNA damage response that leads to cell growth arrest mediated by increased levels of p19(Arf) and p53. Our results show a regulation of NSC expansion driven by a p21/Sox2/p53 axis
Low-Mass Eclipsing Binaries in the Initial Kepler Data Release
We identify 231 objects in the newly released Cycle 0 dataset from the Kepler
Mission as double-eclipse, detached eclipsing binary systems with Teff < 5500 K
and orbital periods shorter than ~32 days. We model each light curve using the
JKTEBOP code with a genetic algorithm to obtain precise values for each system.
We identify 95 new systems with both components below 1.0 M_sun and eclipses of
at least 0.1 magnitudes, suitable for ground-based follow-up. Of these, 14 have
periods less than 1.0 day, 52 have periods between 1.0 and 10.0 days, and 29
have periods greater than 10.0 days. This new sample of main-sequence,
low-mass, double-eclipse, detached eclipsing binary candidates more than
doubles the number of previously known systems, and extends the sample into the
completely heretofore unexplored P > 10.0 day period regime. We find
preliminary evidence from these systems that the radii of low-mass stars in
binary systems decrease with period. This supports the theory that binary
spin-up is the primary cause of inflated radii in low-mass binary systems,
although a full analysis of each system with radial-velocity and multi-color
light curves is needed to fully explore this hypothesis. As well, we present 7
new transiting planet candidates that do not appear among the recently released
list of 706 candidates by the Kepler team, nor in the Kepler False Positive
Catalog, along with several other new and interesting systems. We also present
novel techniques for the identification, period analysis, and modeling of
eclipsing binaries.Comment: 22 pages in emulateapj format. 9 figures, 4 tables, 2 appendices.
Accepted to AJ. Includes a significant addition of new material since last
arXiv submission and an updated method for estimating masses and radi
HAT-P-32b and HAT-P-33b: Two Highly Inflated Hot Jupiters Transiting High-jitter Stars
We report the discovery of two exoplanets transiting high-jitter stars. HAT-P-32b orbits the bright V = 11.289 late-F-early-G dwarf star GSC 3281-00800, with a period P = 2.150008 ± 0.000001 d. The stellar and planetary masses and radii depend on the eccentricity of the system, which is poorly constrained due to the high-velocity jitter (~80 m s^(–1)). Assuming a circular orbit, the star has a mass of 1.16 ± 0.04 M_☉ and radius of 1.22 ± 0.02 R_☉, while the planet has a mass of 0.860 ± 0.164 M_J and a radius of 1.789 ± 0.025 R_J. The second planet, HAT-P-33b, orbits the bright V = 11.188 late-F dwarf star GSC 2461-00988, with a period P = 3.474474 ± 0.000001 d. As for HAT-P-32, the stellar and planetary masses and radii of HAT-P-33 depend on the eccentricity, which is poorly constrained due to the high jitter (~50 m s^(–1)). In this case, spectral line bisector spans (BSs) are significantly anti-correlated with the radial velocity residuals, and we are able to use this correlation to reduce the residual rms to ~35 m s^(–1). We find that the star has a mass of 1.38 ± 0.04 M_☉ and a radius of 1.64 ± 0.03 R_☉ while the planet has a mass of 0.762 ± 0.101 M_J and a radius of 1.686 ± 0.045 R_J for an assumed circular orbit. Due to the large BS variations exhibited by both stars we rely on detailed modeling of the photometric light curves to rule out blend scenarios. Both planets are among the largest radii transiting planets discovered to date
HAT-P-11b: A Super-Neptune Planet Transiting a Bright K Star in the Kepler Field
We report on the discovery of HAT-P-11b, the smallest radius transiting
extrasolar planet (TEP) discovered from the ground, and the first hot Neptune
discovered to date by transit searches. HAT-P-11b orbits the bright (V=9.587)
and metal rich ([Fe=H] = +0.31 +/- 0.05) K4 dwarf star GSC 03561-02092 with P =
4.8878162 +/- 0.0000071 days and produces a transit signal with depth of 4.2
mmag. We present a global analysis of the available photometric and
radial-velocity data that result in stellar and planetary parameters, with
simultaneous treatment of systematic variations. The planet, like its near-twin
GJ 436b, is somewhat larger than Neptune (17Mearth, 3.8Rearth) both in mass Mp
= 0.081 +/- 0.009 MJ (25.8 +/- 2.9 Mearth) and radius Rp = 0.422 +/- 0.014 RJ
(4.73 +/- 0.16 Rearth). HAT-P-11b orbits in an eccentric orbit with e = 0.198
+/- 0.046 and omega = 355.2 +/- 17.3, causing a reflex motion of its parent
star with amplitude 11.6 +/- 1.2 m/s, a challenging detection due to the high
level of chromospheric activity of the parent star. Our ephemeris for the
transit events is Tc = 2454605.89132 +/- 0.00032 (BJD), with duration 0.0957
+/- 0.0012 d, and secondary eclipse epoch of 2454608.96 +/- 0.15 d (BJD). The
basic stellar parameters of the host star are M* = 0.809+0.020-0.027 Msun, R* =
0.752 +/- 0.021 Rsun and Teff = 4780 +/- 50 K. Importantly, HAT-P-11 will lie
on one of the detectors of the forthcoming Kepler mission. We discuss an
interesting constraint on the eccentricity of the system by the transit light
curve and stellar parameters. We also present a blend analysis, that for the
first time treats the case of a blended transiting hot Jupiter mimicing a
transiting hot Neptune, and proves that HAT-P-11b is not such a blend.Comment: Accepted for publication in ApJ, 24 pages, 14 figures, 6 tables. All
RV data presented in this versio
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