The outer regions of the giant Virgo galaxy M87. Kinematic separation of stellar halo and intracluster light

We present a spectroscopic study of 287 Planetary Nebulas (PNs) in a total area of ~0.4 deg^2 around the BCG M87 in Virgo A. With these data we can distinguish the stellar halo from the co-spatial intracluster light (ICL). PNs were identified from their narrow and symmetric redshifted lambda 5007\4959 Angstrom [OIII] emission lines, and the absence of significant continuum. We implement a robust technique to measure the halo velocity dispersion from the projected phase-space to identify PNs associated with the M87 halo and ICL. The velocity distribution of the spectroscopically confirmed PNs is bimodal, containing a narrow component centred on the systemic velocity of the BCG and an off-centred broader component, that we identify as halo and ICL, respectively. Halo and ICPN have different spatial distributions: the halo PNs follow the galaxy's light, whereas the ICPNs are characterised by a shallower power-law profile. The composite PN number density profile shows the superposition of different PN populations associated with the M87 halo and the ICL, characterised by different PN alpha-parameters, the ICL contributing ~3 times more PNs per unit light. Down to m_5007=28.8, the M87 halo PN luminosity function (PNLF) has a steeper slope towards faint magnitudes than the IC PNLF, and both are steeper than the standard PNLF for the M31 bulge. Moreover, the IC PNLF has a dip at ~1-1.5 mag fainter than the bright cutoff, reminiscent of the PNLFs of systems with extended star formation history. The M87 halo and the Virgo ICL are dynamically distinct components with different density profiles and velocity distribution. The different alpha values and PNLF shapes of the halo and ICL indicate distinct parent stellar populations, consistent with the existence of a gradient towards bluer colours at large radii. These results reflect the hierarchical build-up of the Virgo cluster.Comment: 16 pages, 13 figures, 3 tables, A&A, in pres

The Astro-WISE approach to quality control for astronomical data

We present a novel approach to quality control during the processing of astronomical data. Quality control in the Astro-WISE Information System is integral to all aspects of data handing and provides transparent access to quality estimators for all stages of data reduction from the raw image to the final catalog. The implementation of quality control mechanisms relies on the core features in this Astro-WISE Environment (AWE): an object-oriented framework, full data lineage, and both forward and backward chaining. Quality control information can be accessed via the command-line awe-prompt and the web-based Quality-WISE service. The quality control system is described and qualified using archive data from the 8-CCD Wide Field Imager (WFI) instrument (http://www.eso.org/lasilla/instruments/wfi/) on the 2.2-m MPG/ESO telescope at La Silla and (pre-)survey data from the 32-CCD OmegaCAM instrument (http://www.astro-wise.org/~omegacam/) on the VST telescope at Paranal.Comment: Accepted for publication in topical issue of Experimental Astronomy on Astro-WISE information syste

A representative sample of Be stars III: H band spectroscopy

We present H band (1.53 - 1.69 micron) spectra of 57 isolated Be stars of spectral types O9-B9 and luminosity classes III,IV & V. The HI Brackett (n-4) series is seen in emission from Br 11-18, and FeII emission is also apparent for a subset of those stars with HI emission. No emission from species with a higher excitation temperature, such as He II or CIII is seen, and no forbidden line emission is present. A subset of 12 stars show no evidence for emission from any species; these stars appear indistinguishable from normal B stars of a comparable spectral type. In general the line ratios constructed from the transitions in the range Br 11-18 do not fit case B recombination theory particularly well. Strong correlations between the line ratios with Br-gamma and spectral type are found. These results most likely represent systematic variations in the temperature and ionization of the circumstellar disc with spectral type. Weak correlations between the line widths and projected rotational velocity of the stars are observed; however no systematic trend for increasing line width through the Brackett series is observed.Comment: accepted for publication in A&A (this version correctly formatted

Properties and nature of Be stars: 27. Orbital and recent long-term variations of the Pleiades Be star Pleione = BU Tauri

Radial-velocity variations of the H-alpha emission measured on the steep wings of the H-alpha line, prewhitened for the long-time changes, vary periodically with a period of (218.025 +/- 0.022)d, confirming the suspected binary nature of the bright Be star Pleione, a member of the Pleiades cluster. The orbit seems to have a high eccentricity over 0.7, but we also briefly discuss the possibility that the true orbit is circular and that the eccentricity is spurious owing to the phase-dependent effects of the circumstellar matter. The projected angular separation of the spectroscopic orbit is large enough to allow the detection of the binary with large optical interferometers, provided the magnitude difference primary - secondary is not too large. Since our data cover the onset of a new shell phase up to development of a metallic shell spectrum, we also briefly discuss the recent long-term changes. We confirm the formation of a new envelope, coexisting with the previous one, at the onset of the new shell phase. We find that the full width at half maximum of the H-alpha profile has been decreasing with time for both envelopes. In this connection, we briefly discuss Hirata's hypothesis of precessing gaseous disk and possible alternative scenarios of the observed long-term changes

SN 1987A's Circumstellar Envelope, II: Kinematics of the Three Rings and the Diffuse Nebula

We present several different measurements of the velocities of structures within the circumstellar envelope of SN 1987A, including the inner, equatorial ring (ER), outer rings (ORs), and the diffuse nebulosity at radii < 5 pc, based on CTIO 4m and HST data. A comparison of STIS and WFPC2 [N II]6583 loci for the rings show that the ER is expanding in radius at 10.5+-0.3 km/s, with the northern OR expanding along the line of sight at about 26 km/s, and for the southern OR, about 23 km/s. Similar results are found with CTIO 4m data. Accounting for inclination, the best fit to all data show both ORs with an expansion from the SN of 26 km/s. The ratio of the ER to OR velocities is nearly equal to the ratio of ER to OR radii, so the rings are roughly homologous, all having kinematic ages corresponding to about 20,000 yr before the SN explosion. This makes previously reported, large compositional differences between the ER and ORs difficult to understand. Additionally, a grid of longslit 4m/echelle spectra centered on the SN shows two velocity components over a region roughly coextensive with the outer circumstellar envelope extending about 5 pc (20 arcsec) from the SN. One component is blueshifted and the other redshifted from the SN centroid by about 10 km/s each. These features may represent a bipolar flow expanding from the SN, in which the ORs are propelled 10-15 km/s faster than that of the surrounding envelope into which they propogate. The kinematic timescale for the entire nebula is at least about 350,000 yr. The kinematics of these various structures constrain possible models for the evolution of the progenitor and its formation of a mass loss nebula.Comment: 25 pages AASTeX text plus 12 figures. ApJ, in pres

Comparison of the Hα circumstellar disks in Be/X-ray binaries and Be stars

We present a comparative study of the circumstellar disks in Be/X-ray binaries and isolated Be stars based upon the Hα emission line. From this comparison it follows that the overall structure of the disks in the Be/X-ray binaries is similar to the disks of other Be stars, i.e. they are axisymmetric and rotationally supported. The factors for the line broadening (rotation and temperature) in the disks of the Be stars and the Be/X-ray binaries seem to be identical. However, we do detect some intriguing differences between the envelopes. On average, the circumstellar disks of the Be/X-ray binaries are twice as dense as the disks of the isolated Be stars. The different distribution of the Be/X-ray binaries and the Be stars seen in the full with half maximum versus peak separation diagram indicates that the disks in Be/X-ray binaries have on average a smaller size, probably truncated by the compact object.Reig Torres, Pablo, [email protected] ; Fabregat Llueca, Juan, [email protected]

The Be Star HD 215227: A Candidate Gamma-ray Binary

The emission-line Be star HD 215227 lies within the positional error circle of the newly identified gamma-ray source AGL J2241+4454. We present new blue spectra of the star, and we point out the morphological and variability similarities to other Be binaries. An analysis of the available optical photometry indicates a variation with a period of 60.37 +/- 0.04 d, which may correspond to an orbital modulation of the flux from the disk surrounding the Be star. The distance to the star of 2.6 kpc and its relatively large Galactic latitude suggest that the binary was ejected from the plane by a supernova explosion that created the neutron star or black hole companion. The binary and runaway properties of HD 215227 make it an attractive candidate as the optical counterpart of AGL J2241+4454 and as a new member of the small class of gamma-ray emitting binaries.Comment: 14 pages, 3 figures, 1 table. Accepted for publication in ApJ Letters on September 24, 201

Discovery of a Transition to Global Spin-up in EXO 2030+375

EXO 2030+375, a 42-second transient X-ray pulsar with a Be star companion, has been observed to undergo an outburst at nearly every periastron passage for the last 13.5 years. From 1994 through 2002, the global trend in the pulsar spin frequency was spin-down. Using RXTE data from 2003 September, we have observed a transition to global spin-up in EXO 2030+375. Although the spin frequency observations are sparse, the relative spin-up between 2002 June and 2003 September observations, along with an overall brightening of the outbursts since mid 2002 observed with the RXTE ASM, accompanied by an increase in density of the Be disk, indicated by infrared magnitudes, suggest that the pattern observed with BATSE of a roughly constant spin frequency, followed by spin-up, followed by spin-down is repeating. If so this pattern has approximately an 11 year period, similar to the 15 +/- 3 year period derived by Wilson et al. (2002) for the precession period of a one-armed oscillation in the Be disk. If this pattern is indeed repeating, we predict a transition from spin-up to spin-down in 2005.Comment: Accepted for publication in ApJ Letters, 4 pages, 5 figures, using emulateapj.cl

A study of the B and Be star population in the field of the LMC open cluster NGC2004 with VLT-FLAMES

Observations of hot stars belonging to the young cluster LMC-NGC2004 and its surrounding region have been obtained with the VLT-GIRAFFE facilities in MEDUSA mode. 25 Be stars were discovered; the proportion of Be stars compared to B-type stars is found to be of the same order in the LMC and in the Galaxy fields. 23 hot stars were discovered as spectroscopic binaries (SB1 and SB2), 5 of these are found to be eclipsing systems from the MACHO database, with periods of a few days. About 75% of the spectra in our sample are polluted by hydrogen (Halpha and Hgamma), [SII] and [NII] nebular lines. These lines are typical of HII regions. They could be associated with patchy nebulosities with a bi-modal distribution in radial velocity, with higher values (+335 kms^{-1}) preferentially seen inside the southern part of the known bubble LMC4 observed in HI at 21 cm.Comment: 12 pages, 17 figures, accepted to A&

3D simulations of Rayleigh-Taylor mixing in core-collapse SNe with CASTRO

We present multidimensional simulations of the post-explosion hydrodynamics in three different 15 solar mass supernova models with zero, 10^{-4} solar metallicity, and solar metallicities. We follow the growth of the Rayleigh-Taylor instability that mixes together the stellar layers in the wake of the explosion. Models are initialized with spherically symmetric explosions and perturbations are seeded by the grid. Calculations are performed in two-dimensional axisymmetric and three-dimensional Cartesian coordinates using the new Eulerian hydrodynamics code, CASTRO. We find as in previous work, that Rayleigh-Taylor perturbations initially grow faster in 3D than in 2D. As the Rayleigh-Taylor fingers interact with one another, mixing proceeds to a greater degree in 3D than in 2D, reducing the local Atwood number and slowing the growth rate of the instability in 3D relative to 2D. By the time mixing has stopped, the width of the mixed region is similar in 2D and 3D simulations provided the Rayleigh-Taylor fingers show significant interaction. Our results imply that 2D simulations of light curves and nucleosynthesis in supernovae (SNe) that die as red giants may capture the features of an initially spherically symmetric explosion in far less computational time than required by a full 3D simulation. However, capturing large departures from spherical symmetry requires a significantly perturbed explosion. Large scale asymmetries cannot develop through an inverse cascade of merging Rayleigh-Taylor structures; they must arise from asymmetries in the initial explosion.Comment: 12 pages, 5 figures, ApJ accepte