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New insights on the complex planetary nebula Hen 2-113
We report on infrared observations of the planetary nebula Hen 2-113obtained with VLT/NACO, VLTI/MIDI, VLT/ISAAC and TIMMI at the ESO 3.6 m.Hen 2-113 exhibits a clear ring-like structure superimposed to a morediffuse environment visible in the L' (3.8 μm), M' (4.78 μm) and8.7 μm bands. No clear core at 8.7 μm and no fringes through the Nband could be detected for this object with MIDI. A qualitativeinterpretation of the object structure is proposed using a diabolo-likegeometrical model. The PAH content of the nebula was also studied withISAAC and TIMMI observations. This indicates that the PAHs are mostlyconcentrated towards the lobes of the diabolo and the bipolar lobes ofthe nebula. In L' band, a void 0.3 arcsec in diameter was discoveredwith NACO around the central source. The L' and M' fluxes from thecentral source were derived from NACO data indicating an importantinfrared excess with respect to the expected stellar emission based onstellar models and short wavelength data. The observed flux from thissource in the L' and M' is about 300 and 800 times respectively thanthose expected from a model including only the central star. Moreover,the central object appears resolved in L' band with measured FWHM of 155mas. This infrared excess can be explained by emission from a cocoon ofhot dust (T1000 K) with a total mass~10-9~Mȯ.
| A spectroscopic survey for lambda Bootis stars. II. The observational data
lambda Bootis stars comprise only a small number of all A-type stars andare characterized as nonmagnetic, Population i, late B to early F-typedwarfs which show significant underabundances of metals whereas thelight elements (C, N, O and S) are almost normal abundant compared tothe Sun. In the second paper on a spectroscopic survey for lambda Bootisstars, we present the spectral classifications of all program starsobserved. These stars were selected on the basis of their Strömgrenuvbybeta colors as lambda Bootis candidates. In total, 708 objects insix open clusters, the Orion OB1 association and the Galactic field wereclassified. In addition, 9 serendipity non-candidates in the vicinity ofour program stars as well as 15 Guide Star Catalogue stars were observedresulting in a total of 732 classified stars. The 15 objects from theGuide Star Catalogue are part of a program for the classification ofapparent variable stars from the Fine Guidance Sensors of the HubbleSpace Telescope. A grid of 105 MK standard as well as ``pathological''stars guarantees a precise classification. A comparison of our spectralclassification with the extensive work of Abt & Morrell(\cite{Abt95}) shows no significant differences. The derived types are0.23 +/- 0.09 (rms error per measurement) subclasses later and 0.30 +/-0.08 luminosity classes more luminous than those of Abt & Morrell(\cite{Abt95}) based on a sample of 160 objects in common. The estimatederrors of the means are +/- 0.1 subclasses. The characteristics of oursample are discussed in respect to the distribution on the sky, apparentvisual magnitudes and Strömgren uvbybeta colors. Based onobservations from the Observatoire de Haute-Provence, OsservatorioAstronomico di Padova-Asiago, Observatório do Pico dosDias-LNA/CNPq/MCT, Chews Ridge Observatory (MIRA) and University ofToronto Southern Observatory (Las Campanas).
| Three periodic variables of early B spectral type
Using all available uvby observations we find that HR 5375, Sigma Lupi,and HR 6174 are small-amplitude, singly-periodic variables, havingperiods equal to 1.5439, 3.0186 +/- 0.0004, and 1.59416 +/- 0.00013 d,respectively. We point out that while the stars may be ellipsoidalvariables, the existing data are insufficient to rule out two otherhypotheses, namely, those of rotational modulation and high overtoneg-mode pulsations.
| Long-term photometry of variables at ESO. I - The first data catalogue (1982-1986)
This paper presents the catalog of photometric data in the Stromgrensystem obtained during the first four years (October 1982 - September1986) of the Long-Term Photometry of Variables (LTPV) program at ESO.The data are available in computer-readable form.
| UVBY photometry of southern B- and A stars
uvby differential photometry is presented for a number of southern earlytype variable stars. With the exception of Sigma Sco, all stars werepreviously observed during Jerzykiewicz and Sterken's (1977) searchprogram for new southern Beta Cephei type variables. Mean values of thestandard uvby magnitudes and color indices are also provided.
| HD 126859 - A low-amplitude multiperiodic Delta Scuti star
Based on observations obtained with the uvby photometer on the 50-cm ESOtelescope in Chile, the A6V star HD 126859 is found to be a normal mainsequence Delta Scuti star with low amplitude pulsation. A primary periodof 0.0528489 d with an associated full light range of 0.015 m in V isderived, and the secondary period being 0.059694, the period ratio of0.89 suggests either nonradial or high overtone pulsation. No evidencefor a change of the periods in time is found.
| UVBY photometry of the Beta Cephei variable HR 5488
Strömgren photometric measurements of HR 5488 obtained on 19 nightsduring three consecutive years confirm the β Cep character of thestar. Phase dispersion minimization analysis of all observations wasperformed, and three oscillation frequencies were found. The largestamplitude oscillation with frequency f = 7.84004 c/d forms a frequencytriplet with two other small amplitude oscillations. In thec0-β plane, HR 5488 is situated close to the lowerboundary of the β Cep strip.
| Search for Beta Cephei stars south of declination -20 deg. II - Photometric and spectrographic observations of early B giants and subgiants - Winter objects
Results of the second part of a program begun in 1975 (Jerzykiewicz andSterken, 1977) are presented. Out of 39 Beta Cephei candidates observedphotometrically, seven turned out to vary with the b ranges exceeding0.020 m, while 21 have been found constant to within 0.010 m or better.For the 56 comparison stars these numbers are 6 and 25, respectively.From spectrographic observations one of the candidates, HD 129557 = HR5488 (B2 III), iis found to be a Beta Cephei variable with a period of0.135 d and the 2 K amplitude of 18.4 km/s. A comparison of the resultsof this program with other recent photometric searches for Beta Cepheivariables shows good agreement in most cases. There are severaldiscrepant stars, however. These are discussed in some detail. Aconclusion emerges that in the low temperature extension of the BetaCephei region, if such an extension exists at all, on-and-off typepulsations occur.
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