arXiv subjects

L. J. Sánchez

Publications and source records attributed to L. J. Sánchez.

14 recordsLinked to original sources

arXiv2024

CCD Photometry of Trapezia Stars I

We present photometric CCD observations of stars in four stellar trapezia ADS 15184, ADS 4728, ADS 2843, and ADS 16795. This study is performed on images obtained at the Observatorio Astronómico Nacional at San Pedro Mártir (OAN), Baja California, México. In this work we utilise aperture photometry to measure the $U$, $B$, $V$, $R$ and $I$ magnitudes of some of the stars in these dynamically unstable stellar clusters (trapezia). Using the $Q=(U-B)-0.72(B-V)$ parameter we obtained the spectral type of the studied stars as well as their distance to the Sun and their reddening. Slight differences between the $Q$-derived Spectral types and those listed in SIMBAD might be due to a different value, from $0.72$, for the slope of the reddening line on the two-colour diagram.

astro-ph.SR↗

arXiv2023

CCD Photometry of the Globular Cluster NGC 5897

We report CCD photometric observations of the globular cluster NGC 5897, in the Johnson system filters B, V , R, and I. With the values for these magnitudes we obtain various colour indices and produce several colour-magnitude diagrams. We present eight colour-magnitude diagrams: V vs B-V , B vs B-V , V vs V-I, I vs V-I, R vs R-I, I vs R-I, V vs V-R, and R vs V-R. In all of these diagrams we can clearly see the Giant Branch, the Horizontal Branch and the beginning of the Main Sequence. To the left of the Main Sequence turn-off point we detect a somewhat large number of Blue Straggler stars. We determine the mean value of the visual magnitude of the HB as $16.60 \pm 0.46$. This value is fainter than the value found by other authors.

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arXiv2023

New Spectroscopy of U Gem

We present new optical spectroscopic observations of U Geminorum obtained during a quiescent stage. We performed a radial velocity analysis of three Balmer emission lines yielding inconsistent results. Assuming that the radial velocity semi amplitude accurately reflects the motion of the white dwarf, we arrive at masses for the primary which are in the range of M_wd= 1.21 - 1.37 M_Sun. Based on the internal radial velocity inconsistencies and results produced from the Doppler tomography -- wherein we do not detect emission from the hot spot, but rather an intense asymmetric emission overlaying the disc, reminiscent of spiral arms -- we discuss the possibility that the overestimation of the masses may be due to variations of gas opacities and a partial truncation of the disc.

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arXiv2020

New radial velocity observations of AH Her: evidence for material outside the tidal radius

Spectroscopic observations of AH Herculis during a deep quiescent state are put forward. We found the object in a rare long minima, allowing us to derive accurately the semi-amplitudes: $K_1 =121 \pm \, 4$ \kms\ and $K_2 =152 \pm 2$ \kms\ and its mass functions $M_W{ \sin }^{ 3 }i=0.30 \pm 0.01$ M$_{\odot}$ and $M_R{ \sin }^{ 3 }i=0.24 \pm 0.02$ M$_{\odot}$, while its binary separation is given by $a \sin i =1.39 \pm 0.02$~R$_{\odot}$. The orbital period $P_{orb}$~=~ 0.25812~$\pm~0.00032$~days was found from a power spectrum analysis of the radial velocities of the secondary star. These values are consistent with those determined by \citet{Horne:1986}. Our observations indicate that K5 is the most likely spectral type of the secondary. We discuss why we favour the assumption that the donor in AH Her is a slightly evolved star, in which case we find that the best solution for the inclination yields $i = 48^\circ \pm 2^\circ$. Nonetheless, should the donor be a ZAMS star, we obtain that the inclination is between $ i = 43^\circ$ and $i = 44^\circ$. We also present Doppler tomography of H$α$ and H$β$, and found that the emission in both lines is concentrated in a large asymmetric region at low velocities, but at an opposite position to the secondary star, outside the tidal radius and therefore at an unstable position. We also analyse the H$α$ and H$β$ line profiles, which show a single broad peak and compare it with the previous quiescent state study which shows a double-peaked profile, providing evidence for its transient nature.

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arXiv2019

Simultaneous Generalized and Low-Layer SCIDAR turbulence profiles at San Pedro Mártir Observatory

We present optical turbulence profiles obtained with a Generalized SCIDAR (G-SCIDAR) and a Low Layer SCIDAR (LOLAS) at the Observatorio Astronómico Nacional in San Pedro Mártir (OAN-SPM), Baja California, Mexico, during three observing campaigns in 2013, 2014 and 2015. The G-SCIDAR delivers profiles with moderate altitude-resolution (a few hundred meters) along the entire turbulent section of the atmosphere, while the LOLAS gives high altitude-resolution (on the order of tens of meters) but only within the first few hundred meters. Simultaneous measurements were obtained on 2014 and allowed us to characterize in detail the combined effect of the local orography and wind direction on the turbulence distribution close to the ground. At the beginning of several nights, the LOLAS profiles show that turbulence peaks between 25 and 50 m above the ground, not at ground level as was expected. The G-SCIDAR profiles exhibit a peak within the first kilometer. In 55% and 36% of the nights stable layers are detected between 10 and 15 km and at 3 km, respectively. This distribution is consistent with the results obtained with a G-SCIDAR in 1997 and 2000 observing campaigns. Statistics computed with the 7891 profiles that have been measured at the OAN-SPM with a G-SCIDAR in 1997, 2000, 2014 and 2015 campaigns are presented. The seeing values calculated with each of those profiles have a median of 0.79, first and third quartiles of 0.51 and 1.08 arcsec, which are in close agreement with other long term seeing monitoring performed at the OAN-SPM.

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arXiv2019

From outburst to quiescence: spectroscopic evolution of V1838 Aql imbedded in a bow-shock nebula

We analyse new optical spectroscopic, direct-image and X-ray observations of the recently discovered a high proper motion cataclysmic variable V1838 Aql. The data were obtained during its 2013 superoutburst and its subsequent quiescent state. An extended emission around the source was observed up to 30 days after the peak of the superoutburst, interpreted it as a bow--shock formed by a quasi-continuous outflow from the source in quiescence. The head of the bow--shock is coincident with the high--proper motion vector of the source ($v_{\perp}=123\pm5$ km s$^{-1}$) at a distance of $d=202\pm7$ pc. The object was detected as a weak X-ray source ($0.015\pm0.002$ counts s$^{-1}$) in the plateau of the superoutburst, and its flux lowered by two times in quiescence (0.007$\pm$0.002 counts s$^{-1}$). Spectroscopic observations in quiescence we confirmed the orbital period value $P_{\rm{orb}}=0.0545\pm 0.0026$ days, consistent with early-superhump estimates, and the following orbital parameters: $γ= -21\pm3$ km s$^{-1}$ and $K_1 = 53\pm3$ km s$^{-1}$. The white dwarf is revealed as the system approaches quiescence, which enables us to infer the effective temperature of the primary $T_{eff}=11,600\pm400$K. The donor temperature is estimated $\lesssim 2200$K and suggestive of a system approaching the period minimum. Doppler maps in quiescence show the presence of the hot spot in HeI line at the expected accretion disc-stream shock position and an unusual structure of the accretion disc in H$α$.

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arXiv2018

Extensive Photometry of V1838 Aql during the 2013 Superoutburst

We present an in-depth photometric study of the 2013 superoutburst of the recently discovered cataclysmic variable V1838 Aql and subsequent photometry near its quiescent state. A careful examination of the development of the superhumps is presented. Our best determination of the orbital period is Porb = 0.05698(9) days, based on the periodicity of early superhumps. Comparing the superhump periods at stages A and B with the early superhump value we derive a period excess of ε = 0.024(2) and a mass ratio of q = 0.10(1). We suggest that V1838 Aql is approaching the orbital period minimum and thus has a low-mass star as a donor instead of a sub-stellar object.

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arXiv2017

On the dynamical evolution of the Orion Trapezium

We discuss recent observational data on the transverse and radial velocities, as well as on the masses of the main components of the Orion Trapezium. Based on the most reliable values of these quantities we study the dynamical evolution of ensembles of multiple systems mimicking the Orion Trapezium. To this end we conduct numerical $N-$body integrations using the observed masses, planar positions and velocities, radial velocities, and random line-of-sight ($z$) positions for all components. We include perturbations in these quantities compatible with the observational errors. We find the dynamical lifetimes of such systems to be quite short, of the order of 10 to 50 thousand years. The end result of the simulations is usually a tight binary, or sometimes a hierarchical triple. The properties of the evolved systems are studied at different values of the crossing times. The frequency distributions of the major semiaxes and eccentricities of the resulting binaries are discussed and compared with observations.

astro-ph.SR↗

arXiv2016

Variation Of The Tully-Fisher Relation As A Function Of The Magnitude Interval Of A Sample Of Galaxies

In this paper we carry out a preliminary study of the dependence of the Tully-Fisher Relation (TFR) with the width and intensity level of the absolute magnitude interval of a limited sample of 2411 galaxies taken from Mathewson \& Ford (1996). The galaxies in this sample do not differ significantly in morphological type, and are distributed over an $\sim11$-magnitude interval ($-24.4 < I < -13.0$). We take as directives the papers by Nigoche-Netro et al. (2008, 2009, 2010) in which they study the dependence of the Kormendy (KR), the Fundamental Plane (FPR) and the Faber-Jackson Relations (FJR) with the magnitude interval within which the observed galaxies used to derive these relations are contained. We were able to characterise the behaviour of the TFR coefficients $(α, β)$ with respect to the width of the magnitude interval as well as with the brightness of the galaxies within this magnitude interval. We concluded that the TFR for this specific sample of galaxies depends on observational biases caused by arbitrary magnitude cuts, which in turn depend on the width and intensity of the chosen brightness levels.

astro-ph.GA↗

arXiv2013

Kinematics of the Orion Trapezium Based on Diffracto-Astrometry and Historical Data

Using the novel Diffracto-Astrometry technique, we analyze 44 Hubble Space Telescope Wide Field Planetary Camera 2 images of the Orion Trapezium (OT) taken over a span of 12 yr (1995-2007). We measure the relative positions of the six brighter OT components (A-F) and supplement these results with measurements of the relative separations and position angles taken from the literature, thus extending our analysis time base to ~200 yr. For every pair of components we find the relative rate of separation as well as the temporal rate of change of their position angles, which enable us to determine the relative kinematics of the system. Component E shows a velocity larger than the OT's escape velocity, thus confirming that it is escaping from the gravitational pull of this system.

astro-ph.SR↗

arXiv2012

Astroclimate at San Pedro Mártir I: 2004-2008 Seeing Statistics from the TMT Site Testing Data

We present comprehensive seeing statistics for the San Pedro Mártir site derived from the Thirty Meter Telescope site selection data. The observations were obtained between 2004 and 2008 with a Differential Image Motion Monitor (DIMM) and a Multi Aperture Scintillation Sensor (MASS) combined instrument (MASS--DIMM). The parameters that are statistically analised here are: whole atmosphere seeing -measured by the DIMM-; free atmosphere seeing --measured by the MASS--; and ground-layer seeing (GL) --difference between the total and free-atmosphere seeing--. We made a careful data coverage study along with statistical distributions of simultaneous MASS--DIMM seeing measurements, in order to investigate the nightly, monthly, seasonal, annual and global behaviour, as well as possible hourly seeing trends. Although this campaign covers five years, the sampling is uneven, being 2006 and 2007 the best sampled years in terms of seasonal coverage. The overall results yield a median seeing of 0.78 (DIMM), 0.37 (MASS) and 0.59 arcsec (GL). The strongest contribution to the whole atmosphere seeing comes, therefore, from a strong ground layer. We find that the best season is summer, while the worst one is winter, in accordance with previous studies. It is worth noting that the best yearly results are correlated with the best sampled years. The hourly analysis shows that there is no statistically significant tendency of seeing degradation towards dawn. The seeing values are slightly larger than those reported before. This may be caused by climate changes.

astro-ph.IM↗

arXiv2011

An estimate of the temporal fraction of cloud cover at San Pedro Mártir Observatory

San Pedro Mártir in the Northwest of Mexico is the site of the Observatorio Astronómico Nacional. It was one of the five candidates sites for the Thirty Meter Telescope, whose site-testing team spent four years measuring the atmospheric properties on site with a very complete array of instrumentation. Using the public database created by this team, we apply a novel method to solar radiation data to estimate the daytime fraction of time when the sky is clear of clouds. We analyse the diurnal, seasonal and annual cycles of cloud cover. We find that 82.4 per cent of the time the sky is clear of clouds. Our results are consistent with those obtained by other authors, using different methods, adding support to this value and proving the potential of the applied method. The clear conditions at the site are particularly good showing that San Pedro Mártir is an excellent site for optical and infrared observations.

astro-ph.IM↗

arXiv2011

The intrinsic dispersion of the Faber-Jackson relation for early-type galaxies as function of the mass and redshift

Aims. Recently it has been reported that the intrinsic dispersion at constant magnitude of the structural relations from early-type galaxies is a useful tool to study the universality of these structural relations, that is to say, to study whether the structural relations depend on luminosity, wavelength, redshift and/or environment. In this work we study the intrinsic dispersion of the Faber-Jackson relation as function of the luminosity, mass and redshift. Methods. We use a sample of approximately 90 000 early-type galaxies from the Sloan Digital Sky Survey (SDSS-DR7) spanning a magnitude range of 7 $mag$ in both $g$ and $r$ filters. We calculate the intrinsic dispersion of the Faber-Jackson relation at approximately constant magnitude and compare this at different luminosities, masses and redshifts. Results. The main results are the following: i) The intrinsic dispersion of the Faber-Jackson relation depends on the luminosity, mass and redshift. ii) The distribution for brighter and more massive galaxies has smaller intrinsic dispersion than that for fainter and less massive galaxies. iii) The distribution of bright and massive galaxies at higher redshift has smaller intrinsic dispersion than those similar galaxies at low redshift. Conclusions. Comparisons of the results found in this work with recent studies from the literature make us conclude that the intrinsic dispersion of the Faber-Jackson relation could depend on the history of galaxies, in other words, the intrinsic dispersion could depend on the number and nature of transformation events that have affected the galaxies along their life times, such as collapse, accretion, interaction and merging.

astro-ph.CO↗

arXiv2010

The Faber-Jackson relation for early-type galaxies: Dependence on the magnitude range

We take a sample of early-type galaxies from the Sloan Digital Sky Survey (SDSS-DR7, $\sim$ 90 000 galaxies) spanning a range of approximately 7 $mag$ in both $g$ and $r$ filters and analyse the behaviour of the Faber-Jackson relation parameters as functions of the magnitude range. We calculate the parameters in two ways: i) We consider the faintest (brightest) galaxies in each sample and we progressively increase the width of the magnitude interval by inclusion of the brighter (fainter) galaxies (increasing-magnitude-intervals), and ii) we consider narrow-magnitude intervals of the same width ($ΔM = 1.0$ $mag$) over the whole magnitude range available (narrow-magnitude-intervals). Our main results are that: i) in both increasing and narrow-magnitude-intervals the Faber-Jackson relation parameters change systematically, ii) non-parametric tests show that the fluctuations in the values of the slope of the Faber-Jackson relation are not products of chance variations. We conclude that the values of the Faber-Jackson relation parameters depend on the width of the magnitude range and the luminosity of galaxies within the magnitude range. This dependence is caused, to a great extent by the selection effects and because the geometrical shape of the distribution of galaxies on the $M - \log (σ_{0})$ plane depends on luminosity. We therefore emphasize that if the luminosity of galaxies or the width of the magnitude range or both are not taken into consideration when comparing the structural relations of galaxy samples for different wavelengths, environments, redshifts and luminosities, any differences found may be misinterpreted.

astro-ph.CO↗