Primary Observational Distributions of δ Scuti Variables

International Astronomical Union Colloquium ◽

10.1017/s0252921100016353 ◽

2002 ◽

Vol 185 ◽

pp. 324-325

Author(s):

E. Rodríguez ◽

M. Breger

Keyword(s):

High Amplitude ◽

Visual Magnitude ◽

Long Term Monitoring ◽

Low Amplitude ◽

Term Monitoring

The distribution of the known δ Scuti-type variables (R00 catalogue, Rodríguez et al., 2000) is analysed on the basis of some primary observational properties such as visual amplitude, period, visual magnitude and rotational velocities. The present distributions are also compared with those resulting from the earlier catalogue by Rodríguez et al. (1994, R94). The contributions from the Hipparcos, OGLE and MACHO long-term monitoring projects are also discussed. These contributions are quite different in the N-ΔV and N-V diagrams, in the sense that the variables discovered by the Hipparcos satellite are much brighter and with shorter periods than those discovered by the OGLE and MACHO projects.Concerning the N-ΔV diagram, we find that the gap, which was evident in the R94 catalogue for variables with visual amplitudes between 0.m1 to 0.m3, has disappeared. Thus, it seems that there is not a strict separation in two groups relative to the amplitude (low amplitude for variables with ΔV<0.m1 and high amplitude for variables with ΔV>0.m3) for the δ Scuti-type pulsatore.

Download Full-text

Optical and UV investigation of the envelope of AG Carinae

International Astronomical Union Colloquium ◽

10.1017/s0252921100004577 ◽

1989 ◽

Vol 113 ◽

pp. 268-270

Author(s):

Roberto Viotti ◽

Aldo Altamore ◽

Corinne Rossi ◽

Angelo Cassatella

Keyword(s):

Stellar Atmosphere ◽

Spectral Changes ◽

Ring Nebula ◽

Type Spectrum ◽

Visual Magnitude ◽

Long Term Monitoring ◽

Spectral Ranges ◽

Term Monitoring ◽

Critical Structure

The galactic LBV object AG Car is unique for assembling several interesting features: (i) a light curve typical of Hubble-Sandage variables, (ii) a largely variable P Cygni-type spectrum, (iii) a strong IR excess, and especially (iv) a smallring nebula. Caputo and Viotti (1970) found that during 1949-59 the AG Car spectrum varied betweenA1andB0equivalent spectral types. A dramatic evolution occurred in recent years, when the visual magnitude gradually faded from V=6 in 1981 to V=8 in 1985, followed by a rise of the line excitation fromAeqin 1981 (Wolf and Stahl 1982), toBeqin 1983 (Viotti et al. 1984), and to0fpe/WN9in January 1985 (Stahl 1986). This behaviour has represented a unique chance to follow a LBV in different spectral ranges during its major photometric and spectral changes. In the following we present the results of a long term monitoring of the star and of its nebula in the optical and UV. We propose thatAG Car evolved in recent times from a red supergiant phase, and that the present LBV phase is characterized by acritical structureof the stellar atmosphere.

Download Full-text

On the origin of methanol maser variability: Clues from long-term monitoring

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317010523 ◽

2017 ◽

Vol 13 (S336) ◽

pp. 41-44

Author(s):

M. Szymczak ◽

M. Olech ◽

R. Sarniak ◽

P. Wolak ◽

A. Bartkiewicz

Keyword(s):

Binary Systems ◽

High Amplitude ◽

Young Stellar Objects ◽

High Mass ◽

Pumping Rate ◽

Methanol Maser ◽

Bolometric Luminosity ◽

Long Term Monitoring ◽

Term Monitoring

AbstractHigh-mass young stellar objects (HMYSO) displaying methanol maser flux variability probably trace a variety of phenomena such as accretion events, magnetospheric activity, stellar flares and stellar wind interactions in binary systems. A long-term monitoring of the 6.7 GHz methanol line in a large sample of HMYSOs has been undertaken to characterize the variability patterns and examine their origins. The majority of the masers show significant variability on time-scales between a week and a few years. High amplitude short flares of individual features occurred in several HMYSOs. The maser features with low luminosity tend to be more variable than those with high luminosity. The variability of the maser features increases when the bolometric luminosity the powering star decreases. Statistical analysis of basic properties of exciting objects and the variability measures supports an idea that burst activity of methanol masers is driven mainly by changes in the infrared pumping rate.

Download Full-text