2019: February March May June July August

February 2019

Abstract: This paper presents spectroscopic orbits of three binaries, HD 121212, HD 148434 and HD 148912, with evolved primaries and periods of order a year, found in a survey of late-type stars listed in the Supplement to the Yale Bright Star Catalog. All the orbits were determined from observations made with the DAO 1.2-m telescope and coudé spectrograph. Observations were obtained using the radial velocity spectrometer until it was decommissioned in 2004, and since then using a CCD detector and cross-correlating the spectra with those of standard stars.

March 2019

Abstract: We present a search and study of interstellar (IS) absorption features in the observed spectra of two Novae V339 Del and V5668 Sgr. We obtained high resolution spectra ($R\approx 20,000$) in the wavelength range between 3800 and 8800 \AA\ of both novae with the TIGRE telescope. Common IS features of \ion{Na}{i} and \ion{Ca}{ii} were identified in both novae, and the \ion{Ca}{ii} H and K features of Nova V339 Del show substructures, while a blueshifted absorption feature was found in the spectra of Nova V5668 Sgr. Absorption of \ion{K}{i} was identified only in the spectra of Nova V5668 Sgr. The DIBs 6196, 6203, 6379, 6614 and 7562 were found in both novae, and in the spectra of Nova V5668 Sgr we could also identify the DIBs 5780, 5797 and 6660. We present the equivalent widths of all features and determined the column densities of \ion{Ca}{ii}, \ion{K}{i} and hydrogen in the direction of Nova V5668 Sgr ($\log{N_\mathrm{Ca\,II}} = 12.50$, $\log{N_\mathrm{K\,I}} = 11.55$, $\log{N_\mathrm{H}} = 18.5$).

May 2019

Abstract: We have studied the comparative importance of the relativistic beaming model (RBM) and the density variation model (DVM) in our understanding of asymmetries in double radio sources, using their lobe separation ratio (Q) and flux density ratio (F). Our result shows an $F-Q$ correlation in the sense expected for the RBM but contrary to the DVM. We attributed the result for the DVM to varying beam power, as its efficiency is density profile-dependent. From the core-dominant parameter-linear size $R-D$ relation for the RBM subsample, we found that sources in this subsample are beamed within an optimum cone angle $\phi_c\sim 8^{\circ}$.We posit that relativistic beaming is largely accountable for the observed structural asymmetries in radio sources, though other effects cannot be ruled out.

Abstract: In this work, we present models of massive stars between 15 and 23~$M_{\odot}$, with enhanced mass loss rates during the red supergiant phase. Our aim is to explore the impact of extreme red supergiant mass-loss on stellar evolution and on their circumstellar medium. We computed a set of numerical experiments, on the evolution of single stars with initial masses of 15, 18, 20 and, 23~$M_{\odot}$, and solar composition (Z=0.014), using the numerical stellar code BEC. From these evolutionary models, we obtained time-dependent stellar wind parameters, that were used explicitly as inner boundary conditions in the hydrodynamical code ZEUS-3D, which simulates the gas dynamics in the circumstellar medium (CSM), thus coupling the stellar evolution to the dynamics of the CSM. We found that stars with extreme mass loss in the RSG phase behave as a larger mass stars.

Abstract: Minimizing fuel consumption in space travels is becoming increasingly important for spatial development. In the present paper, the fuel consumption in orbit transfers (without gravitational assistance) is minimized, where a spacecraft performs a change from an orbit around the Earth to another one around a different celestial body. Two methods are presented: one of immediate transfer and another with wait time. Minimizing is done by solving a nonlinear system, obtained by applying Lagrange multipliers to the equation modelling the keplerian system, and using the seeds coming from the particle swarm algorithm to execute the Newton's method. Numerical simulations with real values were made to compare these methods with the Hohmann transfer and data from the specialized literature.

Abstract: In this work, I construct a LRG (Luminous Red Galaxy) sample with the redshift of \(0.6\leq z \leq 0.75\) from the Sloan Digital Sky Survey Data Release 15 (SDSS DR15), which contains 184172 CMASS LRGs and 27158 eBOSS LRGs and examine the environmental dependence of galaxy age and stellar mass in this galaxy sample. I divide this LRG sample into subsamples with a redshift binning size of \(\Delta z=0.01\), and analyze the environmental dependence of galaxy age and stellar mass for these subsamples in each redshift bin. Overall, galaxy age and stellar mass in LRG sample with the redshift of \(0.6\leq z \leq 0.75\) are very weakly correlated with the local environment, which shows that minimal environmental dependence of galaxy parameters can continue to higher redshifts.

Abstract: Using $\uv$ photoelectric photometry obtained from the 0.84 m telescope of the Observatorio Astr\'onomico Nacional de San Pedro M\'artir, M\'exico, we have determined some of the physical characteristics, effective temperature and surface gravity of the High Amplitude Delta Scuti star V2455 Cyg (=HD~204615). With newly determined times of maximum light gathered at the Observatorio Astr\'onomico Nacional de Tonantzintla, M\'exico with small 10" telescopes provided with CCD cameras combined with times of maxima in the literature, we have studied the secular variation of the pulsational period of the star.

Abstract: uvby-β photoelectric photometry of sixty-five stars in the direction of the open cluster NGC 1528 is presented. From the uvby-β photometry of the cluster we classified the spectral types of the stars which allowed us to determine the reddening (E(b-y) of $0.196 \pm 0.054$) and hence, their distance, in parsecs, of ($954 \pm 154$). We determined membership of the stars to the cluster and the age (Log age equal 8.04) of the cluster. A metallicity [Fe/H] of $-0.31 \pm 0.08$ was calculated.

Abstract: We present 3D hydrodynamical simulations of the circumstellar bubble from a Wolf-Rayet runaway star. In the models two properties were taken into account: (a) the proper motion of the central star through the interstellar medium (ISM) and (b) the evolution of the stellar wind from the red supergiant (RSG) stage to the Wolf-Rayet (WR) stage. From the hydrodynamic results synthetic X-ray maps in the [0.3-1.2] keV energy range were computed. These maps show that the bubble morphology is affected by the stellar motion, producing a bow shock in the RSG stage that can explain the limb-brightened morphology observed. Additionally, these synthetic maps show filamentary and clumpy appearance produced by instabilities triggered from the interaction between the WR wind and the RSG shell. It was found that these types of collisions can explain the origin of the X-ray emission observed in the nebulae of Wolf- Rayet stars.

June 2019

Abstract: The open cluster Upgren 1 presents peculiar features that in the past led to divergent opinions about its existence. In previous studies on other clusters, uvby − β photoelectric photometry has shown results in agreement with other techniques; therefore, the photometry obtained in the present work has been combined with data from previous studies to examine the brightest stars in the direction of the cluster. On analyzing the unreddened indexes, we found that all the stars are late spectral types. Applying the empirical relations of Nissen (1987) to determine the reddening and, consequently, the unreddened indexes, we found that all but three are located at a distance of $123 \pm 17$ pc. The assigned membership in this study is in concordance with that of Upgren, Philip and Beaver (1982) obtained through radial velocities.

Abstract: The recent success of the Dark Matter model has proven to be an invaluable tool for describing the formation, evolution and stability of galaxies. In this work we study the enhancement function, F, of the gravitational lensing of gravitational waves by Galactic Dark matter halos and show how this function may be used to distinguish between halo models. In particular we compare an isothermal sphere with an NFW type density distribution, both of which are assumed spherically symmetric, and find that our technique clearly distinguishes between the models.

Abstract: In this article, we present the results of a fourth order perturbation analysis of the metric theory of gravity f$(\chi) = \chi^{3/2}$, with $\chi$ a suitable dimensionless Ricci scalar. Such model corresponds to a specific f(R) metric theory of gravity, where the mass of the system is included into the gravitational field's action. In previous works we have shown that, up to the second order in perturbations, this theory reproduces flat rotation curves of galaxies and the details of the gravitational lensing in individual, groups and clusters of galaxies. Here, leaving fixed the results from our previous works, we show that the theory reproduces the dynamical masses of 12 Chandra X-ray galaxy clusters, without the need of dark matter, through the metric coefficients up to the fourth order of approximation. In this sense, we calculate the first relativistic correction of the f($\chi$) metric theory and apply it to fit the dynamical masses of the clusters of galaxies.

July 2019

Abstract: Metallicity gradients derived from planetary nebulae (PNe) using O, Ne, and Ar abundances are studied and compared to those from HII regions in the galaxies M31, M33, NGC300 and the Milky Way. Galactocentric radii and chemical abundances were collected from the literature, carefully selecting a homogeneous sample for each galaxy. Metallicity gradients shown by PNe are flatter than those of HII regions in all cases. The extreme case is M31 where PN abundances are not related to galactocentric distances and the gradients are consistent with zero. To analyze the evolution of gradients with time we build gradients for Peimbert Type I and non-Type I PNe finding that Type I PNe show steeper gradients than non-Type I PNe and more similar to the ones of HII regions indicating that the chemical gradients might steepen with time. Alternatively, the flat gradients for old PNe show that radial migration could have an important role in the evolution of galaxies.

Abstract: In this work, we explore the idea that substructures like stellar clusters could be formed from the tidal stream produced in galactic minor mergers. We use N-body and SPH simulations of satellite galaxies interacting with a larger galaxy. We study the distribution of mass in streams to identify overdensity regions in which a substructure could be formed. We found that without gas, no substructure formed as none of the overdensities shows a definite morphology nor dynamical stability. Including gas we found that several clumps appear and proved to be real long standing physical structures (t $\geq$ 1 Gyr). We analyzed the orbits, ages and masses of these structures, finding its correspondence with the halo subsystems. We conclude that it is possible to form cluster-like structures from the material in tidal streams and found evidence in favour of the presence of dark matter in these systems.

Abstract: We analyze the molecular gas and dust associated with the infrared dark cloud SDC 341.232-0.268 in order to investigate the characteristics and parameters of the gas, determine the evolutionary status of four embedded EGO candidates and establish possible infall or outflow gas motions. We based our study on $^{12}$CO(2-1), $^{13}$CO(2-1), and C$^{18}$O(2-1) data obtained with the APEX telescope, molecular data of high density tracers from the MALT90 survey and IR images from Spitzer, Herschel and ATLASGAL. The study reveals two clumps at -44 km s$^{-1}$ towards the IRDC, with densities of $>$10$^4$cm$^{-3}$, typical of IRDCs, while high density tracers show H$_2$ densities $>$ 10$^{5}$. FIR images reveals the presence of cold dust linked to the molecular clumps and EGOs. A comparison of spectra of the optically thin and optically thick molecular lines towards the EGOs suggests the existence of infall and outflow motions.

Abstract: In this paper it is proposed to search for mid-range planar orbits for a spacecraft traveling in the neighborhood of Deimos. The first task is to perform a numerical search to find and classify mid-range natural orbits around Deimos that are dominated by Mars, using the idea of "Quasi Satellite Orbits" (QSO). The influence of the eccentricity of the orbit of Deimos around Mars and the irregular shape of Mars are considered in the mathematical model, so it is possible to identify their importance, individually. This problem is approached by using two different initial positions for Deimos in its orbit around Mars, the apoapsis and the periapsis. It was also mapped the minimum, maximum, and averaged Deimos-spacecraft distances.

August 2019

Abstract: This paper aims to verify the influence of the bar, its pattern speed ($\Omega_b$) and rate of growth on the stability of the orbits in gravitational potentials. We studied the nature of the orbits in potentials representing galaxies with growing bars, where a linear growth was assumed. In order to study the stability of the orbits we applied SALI. We studied six models in which the bar dimensions were fixed, but we varied their pattern speed and time of bar growth. We found evidence that when the bar growth is faster, more chaos is generated and we also noted that the higher the $\Omega_b$, the greater its influence on the system dynamics. The initial positions of the orbits that have become chaotic are located in a well-defined ring-like region, confined between the ILR and CR resonances. There was also an indication that the retrograde orbits, although much scarcer, seem more conducive to chaos when they do exist.

Abstract: Time-series VI CCD photometry of the globular cluster NGC 1261 is employed to study its variable star population. A membership analysis of most variables based on Gaia~DR2 proper motions and colours was performed prior to the estimation of the mean cluster distance and metallicity. The light curves of the member RR Lyrae were Fourier decomposed to calculate their individual values of distance, [Fe/H], radius and mass. The $I$-band P-L for RR Lyrae stars was also employed. Our best estimates of the metallicity and distance of this Oo I cluster are [Fe/H]$_{\rm ZW}$=$-1.42 \pm 0.05$ dex and $d=17.2 \pm 0.4$ kpc. No mixture of fundamental and first overtone RR Lyrae stars in the either-or or bimodal region is seen in this cluster, as it seems to be the rule for Oo I clusters with a red horizontal branch. A multi-approach search in a region of about $10'\times 10'$ around the cluster revealed no new variable stars within the limitations of our CCD photometry.

Abstract: This paper presents the conceptual design for a new method for the suppression of OH emission lines at near-infrared (NIR) wavelengths by actively adjusting the aperiodic fiber optic Bragg gratings tension. First, we prepared an experimental study in which we simulated an OH emission line using a semiconductor laser at 1548.43 nm and a commercial FBG, with a Bragg wavelength of 1547.76 nm. We demonstrated that the grating Bragg wavelength can be adjusted by controlling the linear deformation of the fiber with a force in the range of 0 to 53.88 gf (0.528 N) that provides a sensitivity of 0.014 nm $g^{-1}$. Second, we proposed the design of a system connected to the telescope instrumentation, with the different stages that would allow monitoring the suppression of emission lines.

Abstract: We report the development of a high-time resolution, 3-colour, simultaneous optical imaging system for the 2.1 m telescope in the San Pedro Mártir Observatory, México. This new instrument, named OPTICAM, will be equipped with three 2,048$\times$2,048 pixel Andor Zyla 4.2-Plus sCMOS cameras and a set of SDSS filters allowing optical coverage in the 320--1,100 nm range. OPTICAM will nominally allow sub-second exposures. However, even higher frame readout speeds can be reached as a function of the pixel array size. Given its instrumental design, a wide range of fast-variability astrophysical sources can be targeted with OPTICAM including X-ray binaries, pulsating white dwarfs, accreting compact objects, eclipsing binaries and exoplanets. OPTICAM observations will be proprietary for only six months and will then be made publicly available to the astronomical community.

Abstract: We present a new database of fully radiative shock models calculated with the shock and photoionization code mappings v. The database architecture is built to contain diverse shock grids comprising of multiple shock parameters. It can be easily accessible through the MySQL protocol. Intensities of spectral lines from infrared to X-rays are stored along with other useful outputs such as the ionic fractions/temperature, integrated densities, etc. A web page was created in order to explore interactively the database as it evolves with time. Examples of its usage are given using the Python language.