Programme ID Research Articles

The offset dependent behavior of narrow optical emission features in the Red Rectangle proto-planetary nebula

Context. The Red Rectangle proto-planetary nebula provides a unique laboratory to study the physical conditions and chemical processes in stellar outflows. Snapshots of the ongoing chemical evolution are obtained by monitoring spectra as function of the offset from the central star. Aims: The focus in this study is on the characterization of narrow optical emission features, that are superimposed on top of extended red emission (ERE). The primary aim is to provide a two-dimensional catalogue of these features for offsets varying from 3'' to 20'' from the central star. Methods: Medium resolution emission spectra for this catalogue have been obtained through optical long-slit measurements using the New Technology Telescope (EMMI-NTT) in La Silla, Chile. Results: The recorded spectra cover the range between 5550 and 6800 A. A complete overview of the central band positions and bandwidths (FWHMs) is provided for both stronger (previously reported) and weaker narrow features. Only some bands are omnipresent in the nebula outflows and other bands only appear further away from the central star. Conclusions: The optical emission bands show intensity variations over the nebula. We suggest that these variations reflect a spatially resolved photochemistry where larger species are photolysed, producing daughter molecules which may be the carriers of the optical emission bands. Based on observations collected at the European Southern Observatory, Chile. Program ID: 080.C-0814(A).

The origin of hydrogen line emission for five Herbig Ae/Be stars spatially resolved by VLTI/AMBER spectro-interferometry

Context: Accretion and outflow processes are of fundamental importance for our understanding of the formation of stars and planetary systems. To trace these processes, diagnostic spectral lines such as the Brγ 2.166 μm line are widely used, although due to a lack of spatial resolution, the origin of the line emission is still unclear. Aims: Employing the AU-scale spatial resolution which can be achieved with infrared long-baseline interferometry, we aim to distinguish between theoretical models which associate the Brγ line emission with mass infall (magnetospheric accretion, gaseous inner disks) or mass outflow processes (stellar winds, X-winds, or disk winds). Methods: Using the VLTI/AMBER instrument, we spatially and spectrally (λ/Δλ = 1500) resolved the inner (⪉5 AU) environment of five Herbig Ae/Be stars (HD 163296, HD 104237, HD 98922, MWC 297, V921 Sco) in the Brγ emission line as well as in the adjacent continuum. From the measured wavelength-dependent visibilities, we derive the characteristic size of the continuum and Brγ line-emitting region. Additional information is provided by the closure phase, which we could measure both in the continuum wavelength regime (for four objects) as well as in the spectrally resolved Brγ emission line (for one object). The spectro-interferometric data is supplemented by archival and new VLT/ISAAC spectroscopy. Results: For all objects (except MWC 297), we measure an increase of visibility within the Brγ emission line, indicating that the Brγ-emitting region in these objects is more compact than the dust sublimation radius. For HD 98922, our quantitative analysis reveals that the line-emitting region is compact enough to be consistent with the magnetospheric accretion scenario. For HD 163296, HD 104237, MWC 297, and V921 Sco we identify an extended stellar wind or a disk wind as the most likely line-emitting mechanism. Since the stars in our sample cover a wide range of stellar parameters, we also search for general trends and find that the size of the Brγ-emitting region does not seem to depend on the basic stellar parameters (such as the stellar luminosity), but correlates with spectroscopic properties, in particular with the Hα line profile shape. Conclusions: By performing the first high-resolution spectro-interferometric survey on Herbig Ae/Be stars, we find evidence for at least two distinct Brγ line-formation mechanisms. Most significant, stars with a P-Cygni Hα line profile and a high mass-accretion rate seem to show particularly compact Brγ-emitting regions (RBrγ/Rcont < 0.2), while stars with a double-peaked or single-peaked Hα-line profile show a significantly more extended Brγ-emitting region (0.6 ⪉ RBrγ/Rcont ⪉ 1.4), possibly tracing a stellar wind or a disk wind. Based on observations made with ESO telescopes at the La Silla Paranal Observatory under open time programme IDs 077.C-0694, 078.C-0360, and 078.C-0680.

Young globular clusters in an old S0: clues to the formation history of NGC 4570

We here present our first attempt to use Globular Clusters as tracers of their parent galaxy’s formation history. Globular Cluster Systems of most early-type galaxies feature two peaks in their optical colour distributions. Blue-peak Globular Clusters are generally believed to be old and metal-poor. The ages, metallicities, and the origin of the red-peak Globular Clusters are being debated. We here present our analysis of the ages and metallicities of the red peak Globular Clusters in the Virgo S0 NGC 4570 using deep Ks-band photometry from NTT/SOFI (ESO program ID 079.B-0511) for the red-peak Globular Clusters in combination with HST-ACS archival data to break the age-metallicity degeneracy. We analyze the combined g, z, and Ks spectral energy distribution by comparison with a large grid of GALEV evolutionary synthesis models for star clusters with different ages and metallicities. This analysis reveals a substantial population of intermediate-age (1–3 Gyr) and metal-rich (� solar metallicity) Globular Clusters. We discuss their age and metallicity distributions together with information on the parent galaxy from the literature to gain insight into the formation history of this galaxy.

First stars

Context: Extremely metal-poor (EMP) stars in the halo of the Galaxy are sensitive probes of the production of the first heavy elements and the efficiency of mixing in the early interstellar medium. The heaviest measurable elements in such stars are our main guides to understanding the nature and astrophysical site(s) of early neutron-capture nucleosynthesis. Aims: Our aim is to measure accurate, homogeneous neutron-capture element abundances for the sample of 32 EMP giant stars studied earlier in this series, including 22 stars with [Fe/H]< -3.0. Methods: Based on high-resolution, high S/N spectra from the ESO VLT/UVES, 1D, LTE model atmospheres, and synthetic spectrum fits, we determine abundances or upper limits for the 16 elements Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, and Yb in all stars. Results: As found earlier, [Sr/Fe], [Y/Fe], [Zr/Fe] and [Ba/Fe] are below Solar in the EMP stars, with very large scatter. However, we find a tight anti-correlation of [Sr/Ba], [Y/Ba], and [Zr/Ba] with [Ba/H] for -4.5 <[Ba/H] < -2.5, also when subtracting the contribution of the main r-process as measured by [Ba/H]. Spectra of even higher S/N ratio are needed to confirm and extend these results below [Fe/H] ? -3.5. The huge, well-characterised scatter of the [n-capture/Fe] ratios in our EMP stars is in stark contrast to the negligible dispersion in the [ ?/Fe] and [Fe-peak/Fe] ratios for the same stars found in Paper V. Conclusions: These results demonstrate that a second (?weak? or LEPP) r-process dominates the production of the lighter neutron-capture elements for [Ba/H] < -2.5. The combination of very consistent [ ?/Fe] and erratic [n-capture/Fe] ratios indicates that inhomogeneous models for the early evolution of the halo are needed. Our accurate data provide strong constraints on future models of the production and mixing of the heavy elements in the early Galaxy. Based on observations made with the ESO Very Large Telescope at Paranal Observatory, Chile (program ID 165.N-0276(A); P.I: R. Cayrel).

The circumbinary disc around the J-type C-star IRAS 18006-3213

Context: In the generally accepted, but poorly documented model, silicate J-type C-stars are binary objects for which the silicate emission originates from a circumbinary or a circumcompanion disc. Aims: We aim at testing this hypothesis by a thorough spectral and spatial observational study of one object: IRAS 18006-3213 . Methods: We obtained, analysed and modeled high spatial resolution interferometric VLTI/MIDI observations on multiple baselines ranging from 45 m to 100 m. Results: All observations resolved the object and show the very compact nature of the N-band emission (~30 mas). In addition, the highest spatial resolution data show a significant differential phase jump around 8.3 mum. This demonstrates the asymmetric nature of the N-band emission. Moreover, the single telescope N-band spectrum shows the signature of highly processed silicate grains. These data are used to confirm the model on silicate J-type C-stars for IRAS 18006-3213 . We show that the most favourable model of the dust geometry is a stable circumbinary disc around the system, seen under an intermediate inclination. Conclusions: The data presented on the silicate J-type C-star IRAS 18006-3213 provide evidence that the oxygen rich dust is trapped in a circumbinary disc. The formation of this disc is probably linked to the binary nature of the central star. Based on observations collected at the European Southern Observatory, Chile. Program ID: 073.D-610(A).

Homogeneous Photometry. V. The Globular Cluster NGC 41471,1Based in part on archival observations made with ESO telescopes at the La Silla and Paranal Observatory under program ID 60.A‐9050(A). 22This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute

ABSTRACTNew BVRI broadband photometry and astrometry are presented for the globular cluster NGC 4147, based upon measurements derived from 524 ground‐based CCD images mostly either donated by colleagues or retrieved from public archives. We have also reanalyzed five exposures of the cluster obtained with WFPC2 on the Hubble Space Telescope in the F439W and F555W (B and V) filters. We present calibrated color‐magnitude and color‐color diagrams. Analysis of the color‐magnitude diagram reveals morphological properties generally consistent with published metal‐abundance estimates for the cluster, and an age typical of other Galactic globular clusters of similar metallicity. We have also redetermined the periods and mean magnitudes for the RR Lyrae variables, including a new c‐type variable reported here for the first time. Our data do not show clear evidence for photometric variability in candidate V18, recently reported by Arellano Ferro et al. (2004, Rev. Mex. A&A, 40, 209). These observations also support the nonvariable status of candidates V5, V9, and V15. The union of our light‐curve data with those of Newburn (, AJ, 62, 197), Mannino (, Mem. Soc. Astron. Italiana, 28, 285), and Arellano Ferro et al. (op. cit.) permits the derivation of significantly improved periods. The mean periods and the Bailey period‐amplitude diagrams support the classification of the cluster as Oosterhoff I, despite its predominantly blue horizontal branch. The number ratio of c‐ to ab‐type RR Lyrae stars, on the other hand, is unusually high for an Oosterhoff I cluster. The calibrated results have been made available through the first author’s Web site.