Detection of a multi-shell planetary nebula around the hot subdwarf O-type star 2MASS J19310888+4324577

(Abridged) The origin of hot subdwarf O-type stars (sdOs) remains unclear since their discovery in 1947. Among others, a post-Asymptotic Giant Branch (post-AGB) origin is possible for a fraction of sdOs. We are involved in a comprehensive ongoing study to search for and to analyze planetary nebulae (PNe) around sdOs with the aim of establishing the fraction and properties of sdOs with a post-AGB origin. We use deep Halpha and [OIII] images of sdOs to detect nebular emission and intermediate resolution, long-slit optical spectroscopy of the detected nebulae and their sdO central stars. These data are complemented with other observations for further analysis of the detected nebulae. We report the detection of an extremely faint, complex PN around 2MASS J19310888+4324577 (2M1931+4324), a star classified as sdO in a binary system. The PN shows a bipolar and an elliptical shell, whose major axes are oriented perpendicular to each other, and high-excitation structures outside the two shells. WISE archive images show faint, extended emission at 12 and 22 microns in the inner nebular regions. The internal nebular kinematics is consistent with a bipolar and a cylindrical/ellipsoidal shell, in both cases with the main axis mainly perpendicular to the line of sight. The nebular spectrum only exhibits Halpha, Hbeta and [OIII]4959,5007 emission lines, but suggests a very low-excitation ([OIII]/Hbeta = 1.5), in strong contrast with the absence of low-excitation emission lines. The spectrum of 2M1931+4324 presents narrow, ionized helium absorptions that confirm the previous sdO classification and suggest an effective temperature >= 60000 K. The binary nature of 2M1931+4324, its association with a complex PN, and several properties of the system provide strong support for the idea that binary central stars are a crucial ingredient in the formation of complex PNe.Comment: 8 pages, 7 figures, accepted in Astronomy and Astrophysic

Bootstrap Selection of the Smoothing Parameter in Nonparametric Hazard Rate Estimation

An asymptotic representation of the mean weighted integrated squared error for the kernel based estimator of the hazard rate in the presence of right censored samples is obtained for different bootstrap resampiing methods. As a consequence, a new bandwidth selector based n the bootstrap is introduced. Very satisfactory simulations results are obtained in comparison to the cross-validation selector for different models, using WARPed, i.e. binned versions of the estimators

Exploring wind direction and SO2 concentration by circular-linear density estimation

The study of environmental problems usually requires the description of variables with different nature and the assessment of relations between them. In this work, an algorithm for flexible estimation of the joint density for a circular-linear variable is proposed. The method is applied for exploring the relation between wind direction and SO2 concentration in a monitoring station close to a power plant located in Galicia (NW-Spain), in order to compare the effectiveness of precautionary measures for pollutants reduction in two different years.Comment: 17 pages, 7 figures, 2 table

Blue Stragglers in Galactic Open Clusters and the Integrated Spectral Energy Distributions

Synthetic integrated spectral properties of the old Galactic open clusters are studies in this work, where twenty-seven Galactic open clusters of ages >= 1Gyr are selected as the working sample. Based on the photometric observations of these open clusters, synthetic integrated spectrum has been made for the stellar population of each cluster. The effects of blue straggler stars (BSSs) on the conventional simple stellar population (SSP) model are analyzed on an individual cluster base. It is shown that the BSSs, whose holding positions in the color-magnitude diagrams (CMDs) cannot be predicted by the current single-star evolution theory, present significant modifications to the integrated properties of theoretical SSP model. The synthesized integrated spectral energy distributions (ISEDs) of our sample clusters are dramatically different from the SSPs based on isochrone only. The BSSs corrected ISEDs of stellar populations show systematic enhancements towards shorter wavelength in the spectra. When measured with wide-band colors in unresolvable conditions, the age of a stellar population can be seriously under-estimated by the conventional SSP model. Therefore, considering the common existence of BSS component in real stellar populations, a considerable amount of alternations on the conventional ISEDs should be expected when applying the technique of evolutionary population synthesis (EPS) to more complicated stellar systems.Comment: 45 pages, 21 figures Accepted for publication in ApJ (Feburary 1, 2005 issue

Identification of new hot subdwarf binary systems by means of Virtual Observatory tools

The estimation of the binary fraction of hot subdwarfs is key to shed light on the different evolution scenarios proposed to explain the loss of the hydrogen envelope during the red giant branch phase. In this paper, we analyse the spectral energy distribution of the hot subdwarfs included in a recent and comprehensive catalogue with the aim of identifying companions. Our methodology shows a performance superior to the photometric criteria used in that study, identifying 202 objects wrongly classified as binaries according to their spectral energy distributions, and finding 269 new binaries. Out of an initial sample of 3186 objects, we classified 2469 as single and 615 as binary hot subdwarfs. The rest of the objects (102) were not classified because of their inadequate spectral energy distribution fitting due, in turn, to poor quality photometry. Effective temperatures, luminosities, and radii were computed for 192 singles and 42 binaries. They, in particular the binary sample, constitute an excellent data set to further perform a more careful spectroscopic analysis that could provide detailed values for the chemical composition, masses, ages, rotation properties, or reflection effects for the shortest period systems. The results obtained in this paper will be used as a reference for a forthcoming work where we aim to generalize binary and single hot subdwarf classification using Artificial Intelligence-based techniques.Agencia Estatal de Investigación | Ref. RTI2018-095076-B-C22Agencia Estatal de Investigación | Ref. PID2020-112949GB-I00Agencia Estatal de Investigación | Ref. MDM-2017-0737Xunta de Galicia | Ref. ED431G 2019/01Xunta de Galicia | Ref. ED481A-2019/155Gobierno de la Comunidad de Madrid | Ref. 2018-T2/TIC-1169

A spectroscopic atlas of post-AGB stars and planetary nebulae selected from the IRAS Point Source Catalogue

Aims: We study the optical spectral properties of a sample of stars showing far infrared colours similar to those of well-known planetary nebulae. The large majority of them were unidentified sources or poorly known in the literature at the time when this spectroscopic survey started, some 15 years ago. Methods: We present low-resolution optical spectroscopy, finding charts and improved astrometric coordinates of a sample of 253 IRAS sources. Results: We have identified 103 sources as post-AGB stars, 21 as ``transition sources'', and 36 as planetary nebulae, some of them strongly reddened. Among the rest of sources in the sample, we were also able to identify 38 young stellar objects, 5 peculiar stars, and 2 Seyfert galaxies. Up to 49 sources in our spectroscopic sample do not show any optical counterpart, and most of them are suggested to be heavily obscured post-AGB stars, rapidly evolving on their way to becoming planetary nebulae. Conclusions: An analysis of the galactic distribution of the sources identified as evolved stars in the sample is presented together with a study of the distribution of these stars in the IRAS two-colour diagram. Finally, the spectral type distribution and other properties of the sources identified as post-AGB in this spectroscopic survey are discussed in the framework of stellar evolution.Comment: 69 pages, 413 figures. Accepted by Astronomy and Astrophysic

The Trithorax protein Ash1L promotes myoblast fusion by activating Cdon expression

Myoblast fusion (MF) is required for muscle growth and repair, and its alteration contributes to muscle diseases. The mechanisms governing this process are incompletely understood, and no epigenetic regulator has been previously described. Ash1L is an epigenetic activator belonging to the Trithorax group of proteins and is involved in FSHD muscular dystrophy, autism and cancer. Its physiological role in skeletal muscle is unknown. Here we report that Ash1L expression is positively correlated with MF and reduced in Duchenne muscular dystrophy. In vivo, ex vivo\ua0and in vitro experiments support a selective and evolutionary conserved requirement for Ash1L in MF. RNA- and ChIP-sequencing indicate that Ash1L is required to counteract Polycomb repressive activity to allow activation of selected myogenesis genes, in particular the key MF gene Cdon. Our results promote Ash1L as\ua0an important epigenetic regulator of MF and suggest that its activity could be targeted to improve cell therapy for muscle diseases