The unprecedented medium-resolution (R~1500-3500) near- and mid-infrared (1-18um) spectrum provided by JWST for the young (140+/-20Myr) low-mass (12-20MJup) L-T transition (L7) companion VHS1256b ...gives access to a catalogue of molecular absorptions. In this study, we present a comprehensive analysis of this dataset utilizing a forward modelling approach, applying our Bayesian framework, ForMoSA. We explore five distinct atmospheric models to assess their performance in estimating key atmospheric parameters: Teff, log(g), M/H, C/O, gamma, fsed, and R. Our findings reveal that each parameter's estimate is significantly influenced by factors such as the wavelength range considered and the model chosen for the fit. This is attributed to systematic errors in the models and their challenges in accurately replicating the complex atmospheric structure of VHS1256b, notably the complexity of its clouds and dust distribution. To propagate the impact of these systematic uncertainties on our atmospheric property estimates, we introduce innovative fitting methodologies based on independent fits performed on different spectral windows. We finally derived a Teff consistent with the spectral type of the target, considering its young age, which is confirmed by our estimate of log(g). Despite the exceptional data quality, attaining robust estimates for chemical abundances M/H and C/O, often employed as indicators of formation history, remains challenging. Nevertheless, the pioneering case of JWST's data for VHS1256b has paved the way for future acquisitions of substellar spectra that will be systematically analyzed to directly compare the properties of these objects and correct the systematics in the models.
A complete accounting of nearby objects -- from the highest-mass white dwarf
progenitors down to low-mass brown dwarfs -- is now possible, thanks to an
almost complete set of trigonometric parallax ...determinations from Gaia,
ground-based surveys, and Spitzer follow-up. We create a census of objects
within a Sun-centered sphere of 20-pc radius and check published literature to
decompose each binary or higher-order system into its separate components. The
result is a volume-limited census of $\sim$3,600 individual star formation
products useful in measuring the initial mass function across the stellar ($<8
M_\odot$) and substellar ($\gtrsim 5 M_{Jup}$) regimes. Comparing our resulting
initial mass function to previous measurements shows good agreement above
0.8$M_\odot$ and a divergence at lower masses. Our 20-pc space densities are
best fit with a quadripartite power law, $\xi(M) = dN/dM \propto M^{-\alpha}$
with long-established values of $\alpha = 2.3$ at high masses ($0.55 < M < 8.00
M_\odot$) and $\alpha = 1.3$ at intermediate masses ($0.22 < M < 0.55
M_\odot$), but at lower masses we find $\alpha = 0.25$ for $0.05 < M <0.22
M_\odot$ and $\alpha = 0.6$ for $0.01 < M < 0.05 M_\odot$. This implies that
the rate of production as a function of decreasing mass diminishes in the
low-mass star/high-mass brown dwarf regime before increasing again in the
low-mass brown dwarf regime. Correcting for completeness, we find a star to
brown dwarf number ratio of, currently, 4:1, and an average mass per object of
0.41 $M_\odot$.
The Sloan Digital Sky Survey IV (SDSS-IV) APOGEE-2 primary science goal was to observe red giant stars throughout the Galaxy to study its dynamics, morphology, and chemical evolution. The APOGEE ...instrument, a high-resolution 300 fiber H-band (1.55-1.71 micron) spectrograph, is also ideal to study other stellar populations in the Galaxy, among which are a number of star forming regions and young open clusters. We present the results of the determination of six stellar properties (\(T_{eff}\), \(\log{g}\), Fe/H, \(L/L_\odot\), \(M/M_\odot\), and ages) for a sample that is composed of 3360 young stars, of sub-solar to super-solar types, in sixteen Galactic star formation and young open cluster regions. Those sources were selected by using a clustering method that removes most of the field contamination. Samples were also refined by removing targets affected by various systematic effects of the parameter determination. The final samples are presented in a comprehensive catalog that includes all six estimated parameters. This overview study also includes parameter spatial distribution maps for all regions and Hertzprung-Russell (\(L/L_\odot\) vs. \(T_{eff}\)) diagrams. This study serves as a guide for detailed studies on individual regions, and paves the way for the future studies on the global properties of stars in the pre-main sequence phase of stellar evolution using more robust samples.
Very young (t \(\lesssim\) 10 Myrs) stars possess strong magnetic fields that channel ionized gas from the interiors of their circumstellar discs to the surface of the star. Upon impacting the ...stellar surface, the shocked gas recombines and emits hydrogen spectral lines. To characterize the density and temperature of the gas within these accretion streams, we measure equivalent widths of Brackett (Br) 11-20 emission lines detected in 1101 APOGEE spectra of 326 likely pre-main sequence accretors. For sources with multiple observations, we measure median epoch-to-epoch line strength variations of 10% in Br11 and 20% in Br20. We also fit the measured line ratios to predictions of radiative transfer models by Kwan & Fischer. We find characteristic best-fit electron densities of \(n_e\) = 10\(^{11} - 10^{12}\) cm\(^{-3}\), and excitation temperatures that are inversely correlated with electron density (from T\(\sim\)5000 K for \(n_e \sim 10^{12}\) cm\(^{-3}\), to T\(\sim\)12500 K at \(n_e \sim 10^{11}\) cm\(^{-3}\)). These physical parameters are in good agreement with predictions from modelling of accretion streams that account for the hydrodynamics and radiative transfer within the accretion stream. We also present a supplementary catalog of line measurements from 9733 spectra of 4255 Brackett emission line sources in the APOGEE DR17 dataset.
Geos Ingenieros es una empresa cajamarquina que brinda servicios de instalación de tuberías HDPE y geosintéticos al sector minero de la región, fue creada el año 2002, su principal cliente fue Minera ...Yanacocha hasta el año 2016 y luego Minera Gold Fields; tiene como fortalezas la sólida experiencia de casi dos décadas de gestión empresarial, ha formado personal técnico especializado del ámbito local, cuentan con equipos y maquinaria de buen desempeño; como oportunidades resaltan el incremento de obras de construcción para el cuidado del medio ambiente con materiales geosintéticos, mayor demanda de servicios luego de la pandemia para reactivar la economía y disminución del costo financiero para alentar la inversión.El propósito de la consultoría fue diagnosticar la situación de la empresa e identificar el problema más relevante, analizar las causas y proponer soluciones que le permitan crecer en el mediano y largo plazo. El problema central encontrado fue que Geos Ingenieros tiene poca eficiencia en la gestión y bajo enfoque en el mercado, se realizó el análisis de causas utilizando el método de Ishikawa y se determinó que la empresa centraliza y sobre carga varias funciones en el gerente general ocasionando una serie de problemas internos; asimismo no se identifican plenamente las necesidades del cliente para ofrecer nuevos servicios.Se ha planteado la implementación de dos alternativas de solución para abordar el problema integral de Geos Ingenieros: (a) enfoque de mercado con el desarrollo de nuevos servicios y la creación del área comercial y (b) implementación de un sistema ERP para centralizar la información y tomar decisiones oportunas.El plan de implementación de las alternativas de solución tomará un plazo de un año y los resultados esperados han sido proyectados hasta el año 2026, donde se muestra que la empresa alcanzará su objetivo de largo plazo en nivel de ventas, rentabilidad y número de contratos de servicios con clientes mineros.
The stellar initial mass function (IMF) is an essential input for many astrophysical studies but only in a few cases it has been determined over the whole cluster mass range, limiting the conclusions ...about its nature. The 25 Orionis group (25 Ori) is an excellent laboratory to investigate the IMF across the entire mass range of the population, from planetary-mass objects to intermediate/high-mass stars. We combine new deep optical photometry with optical and near-infrared data from the literature to select 1687 member candidates covering a 1.1\(^\circ\) radius area in 25 Ori. With this sample we derived the 25 Ori system IMF from 0.012 to 13.1 \(M_\odot\). This system IMF is well described by a two-segment power-law with \(\Gamma=-0.74\pm0.04\) for \(m<0.4\ M_\odot\) and \(\Gamma=1.50\pm0.11\) for \(m\ge0.4\ M_\odot\). It is also well described over the whole mass range by a tapered power-law function with \(\Gamma=1.10\pm0.09\), \(m_p=0.31\pm0.03\) and \(\beta=2.11\pm0.09\). The best lognormal representation of the system IMF has \(m_c=0.31\pm0.04\) and \(\sigma=0.46\pm0.05\) for \(m<1\ M_\odot\). This system IMF does not present significant variations with the radii. We compared the resultant system IMF as well as the BD/star ratio of \(0.16\pm0.03\) we estimated for 25 Ori with that of other stellar regions with diverse conditions and found no significant discrepancies. These results support the idea that general star formation mechanisms are probably not strongly dependent to environmental conditions. We found that the substellar and stellar objects in 25 Ori have similar spatial distributions and confirmed that 25 Ori is a gravitationally unbound stellar association.
We present a large-scale study of stellar rotation for T Tauri stars in the Orion Star-Forming Complex. We use the projected rotational velocity (\(v\sin(i)\)) estimations reported by the APOGEE-2 ...collaboration as well as individual masses and ages derived from the position of the stars in the HR diagram, considering Gaia-EDR3 parallaxes and photometry plus diverse evolutionary models. We find an empirical trend for \(v\sin(i)\) decreasing with age for low-mass stars (\(0.4 M_{\odot} < M_{\ast} < 1.2 M_{\odot}\)). Our results support the existence of a mechanism linking \(v\sin(i)\) to the presence of accreting protoplanetary disks, responsible for regulating stellar rotation in timescales of about 6 Myr, which is the timescale in which most of the T Tauri stars lose their inner disk. Our results provide important constraints to models of rotation in the early phases of evolution of young stars and their disks.
We present \(Spitzer\) IRS 5--14 \(\mu\)m spectra and 16 \(\mu\)m and 22 \(\mu\)m photometry of the T2.5 companion to the \(\sim\)300 Myr-old G0V star HN Peg. We incorporate previous 0.8--5 \(\mu\)m ...observations to obtain the most comprehensive spectral energy distribution of an intermediate-gravity L/T-transition dwarf which, together with an accurate Gaia EDR3 parallax of the primary, enable us to derive precise fundamental parameters. We find that young (\(\approx\)0.1--0.3 Gyr) early-T dwarfs on average have \(\approx\)140 K lower effective temperatures, \(\approx\)20% larger radii, and similar bolometric luminosities compared to \(\gtrsim\)1 Gyr-old field dwarfs with similar spectral types. Our accurate infrared spectrophotometry offers new detail at wavelengths where the dominant carbon-bearing molecules have their strongest transitions: at 3.4 \(\mu\)m for methane and at 4.6 \(\mu\)m for carbon monoxide. We assess the performance of various widely available photospheric models and find that models with condensates and/or clouds better reproduce the full SED of this moderately young early-T dwarf. However, cloud-free models incorporating a more general convective instability treatment reproduce at least the low-resolution near-IR spectrum similarly well. Our analysis of \(R\approx2300\) \(J\)-band spectra shows that the near-infrared potassium absorption lines in HN Peg B have similar strengths to those seen in both younger and older T2-T3 dwarfs. We conclude that while alkali lines are well-established as surface gravity indicators for L-type or warmer stars, they are insensitive to surface gravity in early-T dwarfs
We present spectroscopic observations of the C II $\lambda$6578 permitted
line for 83 lines of sight in 76 planetary nebulae at high spectral resolution,
most of them obtained with the Manchester ...Echelle Spectrograph on the 2.1\,m
telescope at the Observatorio Astron\'omico Nacional on the Sierra San Pedro
M\'artir. We study the kinematics of the C II $\lambda$6578 permitted line with
respect to other permitted and collisionally-excited lines. Statistically, we
find that the kinematics of the C II $\lambda$6578 line are not those expected
if this line arises from the recombination of C$^{2+}$ ions or the fluorescence
of C$^+$ ions in ionization equilibrium in a chemically-homogeneous nebular
plasma, but instead its kinematics are those appropriate for a volume more
internal than expected. The planetary nebulae in this sample have well-defined
morphology and are restricted to a limited range in H$\alpha$ line widths (no
large values) compared to their counterparts in the Milky Way bulge, both of
which could be interpreted as the result of young nebular shells, an inference
that is also supported by nebular modeling. Concerning the long-standing
discrepancy between chemical abundances inferred from permitted and
collisionally-excited emission lines in photoionized nebulae, our results imply
that multiple plasma components occur commonly in planetary nebulae.
The Orion OB1a sub-association is a rich low mass star (LMS) region. Previous spectroscopic studies have confirmed 160 LMSs in the 25 Orionis stellar group (25 Ori), which is the most prominent ...overdensity of Orion OB1a. Nonetheless, the current census of the 25 Ori members is estimated to be less than 50% complete, leaving a large number of members to be still confirmed. We retrieved 172 low-resolution stellar spectra in Orion OB1a observed as ancillary science in the SDSS-III/BOSS survey, for which we classified their spectral types and determined physical parameters. To determine memberships, we analyzed the H\(_\alpha\) emission, LiI\(\lambda\)6708 absorption, and NaI\(\lambda\lambda\)8183, 8195 absorption as youth indicators in stars classified as M-type. We report 50 new LMSs spread across the 25 Orionis, ASCC 18, and ASCC 20 stellar groups with spectral types from M0 to M6, corresponding to a mass range of 0.10\(\le m/\textrm{M}_\odot \le\)0.58. This represents an increase of 50% in the number of known LMSs in the area and a net increase of 20% in the number of 25 Ori members in this mass range. Using parallax values from the Gaia DR1 catalog, we estimated the distances to these three stellar groups and found that they are all co-distant, at 338\(\pm\)66 pc. We analyzed the spectral energy distributions of these LMSs and classified their disks by evolutionary classes. Using H-R diagrams, we found a suggestion that 25 Ori could be slightly older that the other two observed groups in Orion OB1a.
