A search for flares and mass ejections on young late-type stars in the open cluster Blanco-1

We present a search for stellar activity (flares and mass ejections) in a sample of 28 stars in the young open cluster Blanco-1. We use optical spectra obtained with ESO's VIMOS multi-object spectrograph installed on the VLT. From the total observing time of $\sim$ 5 hours, we find four H$\alpha$ flares but no distinct indication of coronal mass ejections (CMEs) on the investigated dK-dM stars. Two flares show "dips" in their light-curves right before their impulsive phases which are similar to previous discoveries in photometric light-curves of active dMe stars. We estimate an upper limit of $<$4 CMEs per day per star and discuss this result with respect to a semi- empirical estimation of the CME rate of main-sequence stars. We find that we should have detected at least one CME per star with a mass of 1-15$\times10^{16}$ g depending on the star's X-ray luminosity, but the estimated H$\alpha$ fluxes associated with these masses are below the detection limit of our observations. We conclude that the parameter which mainly influences the detection of stellar CMEs using the method of Doppler-shifted emission caused by moving plasma is not the spectral resolution or velocity but the flux or mass of the CME.Comment: Accepted for publication in MNRAS, accepted 2014 June 10, received 2014 June 5, in original form 2014 March 24, 14 pages, 5 figure

On the Evolved Nature of CK Vul

Original paper can be found at: http://www.astrosociety.org/pubs/cs/381.html Copyright ASPCK Vul was classified as the oldest observed nova. Recent studies have proven however, that CK Vul cannot be unambiguously classified as any known kind of eruptive variable. We present the optical and radio observations of the remnants of the eruption of CK Vul in the year 1670 in order to discuss possible scenarios for this object. We have measured the proper motion which proves that the nebula is attributed to the star observed during its 1670−1672 brightening. A large bipolar nebula of 70 arcsec is discovered in a deep Hα image. Radio observations reveal a barely resolved source placed in the expansion center of the ejecta

LNCS

Systems ought to behave reasonably even in circumstances that are not anticipated in their specifications. We propose a definition of robustness for liveness specifications which prescribes, for any number of environment assumptions that are violated, a minimal number of system guarantees that must still be fulfilled. This notion of robustness can be formulated and realized using a Generalized Reactivity formula. We present an algorithm for synthesizing robust systems from such formulas. For the important special case of Generalized Reactivity formulas of rank 1, our algorithm improves the complexity of [PPS06] for large specifications with a small number of assumptions and guarantees

The Local Group Census: planetary nebulae in Sextans B

Five planetary nebulae (PNe) have been discovered in the nearby dwarf irregular galaxy. Emission line images were obtained using the Wide Field Camera of the 2.5m Isaac Newton Telescope (INT) at La Palma (Spain). The candidate PNe were identified by their point-like appearance and relatively strong [OIII] emission-line fluxes. They are located within a galactocentric distance of 2.8 arcmin, corresponding to 1.1 kpc at the distance of Sextans B. Luminosities are in the range 1800--5600Lsolar. Sextans B is one of the smallest dwarf irregular galaxies with a PN population. The number of PNe detected suggest an enhanced star formation rate between 1 and 5 Gyr ago.Comment: 7 pages, 2 figure

The new carbon symbiotic star IPHAS J205836.43+503307.2

We are performing a search for symbiotic stars using IPHAS, the INT Halpha survey of the northern Galactic plane, and follow-up observations. Candidate symbiotic stars are selected on the basis of their IPHAS and near-IR colours, and spectroscopy and photometry are obtained to determine their nature. We present here observations of the symbiotic star candidate IPHAS J205836.43+503307.2. The optical spectrum shows the combination of a number of emission lines, among which are the high-excitation species of [OIII], HeII, [Ca V], and [Fe VII], and a red continuum with the features of a star at the cool end of the carbon star sequence. The nebular component is spatially resolved: the analysis of the spatial profile of the [NII]6583 line in the spectrum indicates a linear size of ~2.5 arcsec along the east-west direction. Its velocity structure suggests an aspherical morphology. The near-infrared excess of the source, which was especially strong in 1999, indicated that a thick circumstellar dust shell was also present in the system. The carbon star has brightened in the last decade by two to four magnitudes at red and near-infrared wavelengths. Photometric monitoring during a period of 60 days from November 2010 to January 2011 reveals a slow luminosity decrease of 0.2 magnitudes. From the observed spectrophotometric properties and variability, we conclude that the source is a new Galactic symbiotic star of the D-type, of the rare kind that contains a carbon star, likely a carbon Mira. Only two other systems of this type are known in the Galaxy.Comment: 6 pages, 4 figure

Specification-Centered Robustness

In addition to being correct, a system should be robust, that is, it should behave reasonably even after receiving unexpected inputs. In this paper, we summarize two formal notions of robustness that we have introduced previously for reactive systems. One of the notions is based on assigning costs for failures on a user-provided notion of incorrect transitions in a specification. Here, we define a system to be robust if a finite number of incorrect inputs does not lead to an infinite number of incorrect outputs. We also give a more refined notion of robustness that aims to minimize the ratio of output failures to input failures. The second notion is aimed at liveness. In contrast to the previous notion, it has no concept of recovery from an error. Instead, it compares the ratio of the number of liveness constraints that the system violates to the number of liveness constraints that the environment violates

The Local Group Census: planetary nebulae in IC 10, Leo A and Sextans A

In the framework of our narrow-band survey of the Local Group galaxies, we present the results of the search for planetary nebulae (PNe) in the dwarf irregular galaxies IC10, LeoA and SextansA. Using the standard on-band/off-band technique, sixteen new candidate PNe have been discovered in the closest starburst galaxy, IC10. The optical size of this galaxy is estimated to be much larger than previously thought, considering the location of the new PNe in an area of 3.6 kpc X 2.7 kpc. We also confirm the results of previous studies for the other two dwarf irregular galaxies, with the detection of one candidate PN in LeoA and another one in SextansA. We review the number of planetary nebulae discovered in the Local Group to date and their behaviour with metallicity. We suggest a possible fall in the observed number of PNe when [Fe/H]$<<$-1.0, which might indicate that below this point the formation rate of PNe is much lower than for stellar populations of near Solar abundances. We also find non-negligible metallicity effects on the [OIII] luminosity of the brightest PN of a galaxy.Comment: 10 pages, 4 figures, A&A accepte