S. G. Navarro

Automatic spectral classification of stellar spectra with low signal-to-noise ratio using artificial neural networks

Context. As part of a project aimed at deriving extinction-distances for thirty-five planetary nebulae, spectra of a few thousand stars were analyzed to determine their spectral type and luminosity class. Aims. We present here the automatic spectral classification process used to classify stellar spectra. This system can be used to classify any other stellar spectra with similar or higher signal-to-noise ratios. Methods. Spectral classification was performed using a system of artificial neural networks that were trained with a set of line-strength indices selected among the spectral lines most sensitive to temperature and the best luminosity tracers. The training and validation processes of the neural networks are discussed and the results of additional validation probes, designed to ensure the accuracy of the spectral classification, are presented. Results. Our system permits the classification of stellar spectra of signal-to-noise ratio (S /N) significantly lower than it is generally considered to be needed. For S /N ≥ 20, a precision generally better than two spectral subtypes is obtained. At S /N < 20, classification is still possible but has a lower precision. Its potential to identify peculiar sources, such as emission-line stars, is also recognized.

Spitzer mid-infrared spectroscopic observations of planetary nebulae

We present Spitzer Space Telescope archival mid-infrared (mid-IR) spectroscopy of a sample of eleven planetary nebulae (PNe). The observations, acquired with the Spitzer Infrared Spectrograph (IRS), cover the spectral range 5.2-14.5 {\mu}m that includes the H2 0-0 S(2) to S(7) rotational emission lines. This wavelength coverage has allowed us to derive the Boltzmann distribution and calculate the H2 rotational excitation temperature (Tex). The derived excitation temperatures have consistent values ~900+/-70 K for different sources despite their different structural components. We also report the detection of mid-IR ionic lines of [Ar III], [S IV], and [Ne II] in most objects, and polycyclic aromatic hydrocarbon (PAH) features in a few cases. The decline of the [Ar III]/[Ne II] line ratio with the stellar effective temperature can be explained either by a true neon enrichment or by high density circumstellar regions of PNe that presumably descend from higher mass progenitor stars.

Millimetre polarization of the protoplanetary nebula OH 231.8+4.2: a follow-up study with CARMA

In order to investigate the characteristics and influence of the magnetic field in evolved stars, we performed a follow-up investigation of our previous submillimeter analysis of the proto-planetary nebula (PPN) OH 231.8+4.2 (Sabin et al. 2014), this time at 1.3 mm with the CARMA facility in polarisation mode for the purpose of a multi-scale analysis. OH 231.8+4.2 was observed at �2.5 ′′ resolution and we detected polarised emission above the 3σ threshold (with a mean polarisation fraction of 3.5%). The polarisation map indicates an overall organised magnetic field within the nebula. The main finding i n this paper is the presence of a structure mostly compatible with an ordered toroidal component that is aligned with the PPN’s dark lane. We also present some alternative magnetic fi eld configuration to explain the structure observed. These data complete our previous SMA submillimeter data for a better investigation and understanding of the magnetic field struc ture in OH 231.8+4.2.

Dark matter inside early-type galaxies as function of mass and redshift

We study the behaviour of the dynamical and stellar mass inside the effective radius (re) of early-type galaxies (ETGs). We use several samples of ETGs -ranging from 19 000 to 98 000 objects- from the ninth data release of the Sloan Digital Sky Survey. We consider Newtonian dynamics, different light profiles and different Initial Mass Functions (IMF) to calculate the dynamical and stellar mass. We assume that any difference between these two masses is due to dark matter and/or a non Universal IMF. The main results for galaxies in the redshift range 0.0024 < z < 0.3500 and in the dynamical mass range 9.5 < log(M) < 12.5 are: i) A significant part of the intrinsic dispersion of the distribution of dynamical vs. stellar mass is due to redshift. ii) The difference between dynamical and stellar mass increases as a function of dynamical mass and decreases as a function of redshift. iii) The difference between dynamical and stellar mass goes from approximately 0% to 70% of the dynamical mass depending on mass and redshift. iv) These differences could be due to dark matter or a non Universal IMF or a combination of both. v) The amount of dark matter inside ETGs would be equal to or less than the difference between dynamical and stellar mass depending on the impact of the IMF on the stellar mass estimation. vi) The previous results go in the same direction of some results of the Fundamental Plane (FP) found in the literature in the sense that they could be interpreted as an increase of dark matter along the FP and a dependence of the FP on redshift.

The tidal filament of NGC 4660

NGC 4660, in the Virgo cluster, is a well-studied elliptical galaxy which has a strong disk component (D/T approximately 0.2–0.3). The central regions, including the disk component, have stellar populations approximately 12–13 Gyr in age, based on SAURON studies. However, we report the discovery of a long, narrow tidal filament associated with the galaxy, as seen in deep co-added Schmidt plate images and deep CCD frames, implying that the galaxy has undergone a tidal interaction and merger within the last few Gyr. The relative narrowness of the filament implies a wet merger with at least one spiral galaxy involved, but the current state of the system shows little evidence of such. However, a two-component photometric fit using GALFIT shows much bluer colors for the disk component than for the elliptical component, which may represent a residual trace of enhanced star formation in the disk caused by the interaction 1–2 Gyr ago. There are brighter concentrations within the filament that resemble tidal dwarf galaxies, although they are at least 40 times fainter. These concentrations may represent faint, evolved versions of those galaxies. A previously detected stripped satellite galaxy south of the nucleus seen in our residual image may imply that the filament is a tidal stream produced by perigalactic passages of this satellite.

Stellar longitudinal magnetic field determination through multi-Zeeman signatures

Context. A lot of effort has been put into the detection and determination of stellar magnetic fields using the spectral signal obtained from the combination of hundreds or thousands of individual lines, an approach known as a multi-line analysis. So far, however, most of the developed multi-line techniques that retrieve mean stellar longitudinal magnetic fields can sometimes entail substantial simplifications concerning line shapes and Zeeman splittings. Aims. In this paper we determine stellar longitudinal magnetic fields by means of the Principal Components Analysis and Zeeman Doppler Imaging (PCA-ZDI) multi-line technique, based on accurate polarised spectral line synthesis. Methods. In this paper we present the methodology for performing inversions of profiles obtained using PCA-ZDI. Results. Inversions with various magnetic geometries, field strengths and rotational velocities show that we can correctly determine the effective longitudinal magnetic field in stars using the PCA-ZDI method.

Jets in Symbiotic Stars: The R Aqr Case

In this paper we analyse the jet like features observed in some symbiotic systems, we present the objects in which such features were detected. One of this objects is R Aqr. In this object high collimated outflows emerging from the central region has been observed since the 1970s. We present the possible explanation for this outflows and analyse some new kinematic data of this object comparing them with previous observations.

Optics and the mechanical system of the 62-cm telescope at the Severo Díaz Galindo Observatory in Guadalajara, Jalisco, México

We present the results of a modification performed in the optical system of the 62 cm telescope (f/14.32) at observatory “Severo Díaz Galindo” Universidad de Guadalajara, Mexico. This modification consists of a change of distance between the primary and secondary mirrors from 1020 to 1135 mm. With this, a change in the image plane from 5200 mm to 600 mm, measured from the vertex of the primary mirror, is obtained. The latter allow to get the first astronomical images of The Telescope. This modification was necessary because alignment errors, such as distance between primary and secondary mirrors in the original system were presented. Besides, the telescope has a new accurate and adequate mechanical system installed on November 2011. Details and the first images obtained, are here presented.

Distance determination to PNe using the extinction-distance method

We present individual distances to three PNe: NGC 6537, NGC 6781 and NGC 7027, determined by the extinction-distance method. These objects are part of a larger sample (35) of PNe that we observed at ORM. In order to apply this method, and to obtain accurate distances, we determined the spectral type of 40 to 60 stars in the line of sight of each PNe. This implied the necessity of classifying few thousands of stellar spectra with S/N ratio between 10 and 60. To solve such need we developed an ANN system to perform automatic spectral classification which could classify spectra with S/N ratio as low as 20 with an accuracy better than 2 spectral subtypes. In this poster we compare the accuracy of such distances with previous distance determinations using other methods. We conclude that it is possible to use this method to obtain the distance of a large number of PNe with better precision.