2019 Valencia

GEOS meeting in Valencia showcases advances in Variable Star research and collaboration

Astronomers gather to present new tools, scientific results, and foster professional-amateur partnerships in the study of variable stars.

The annual GEOS meeting held in Valencia on 31 May and 1 June 2019 brought together professional and amateur astronomers to share the latest developments in variable star research and to strengthen collaborative efforts within the community.

Among the highlights was the presentation of the “AAVSO-Charts” software by Laurent Corp, designed to streamline the process of obtaining field maps and comparison star magnitudes for variable star observations. This tool significantly reduces the time and effort required by observers, making photometric work more accessible and efficient.

Juan Fabregat outlined the scientific objectives of the GEOS priority programme on Be stars, focusing on the long-term monitoring of their variability and the detection of outburst activity. He also revisited the historic GEOS observations of the Be star OT Gem, offering new interpretations in light of current knowledge about non-radial pulsations and proposing future observational campaigns.

Stéphane Ferrand presented an in-depth study of the red star RY UMi, highlighting semi-periodic variations detected through an intensive visual survey. J.F. Le Borgne discussed the investigation of two suspected RR Lyrae variables (NSV 14264 and NSV 14172), concluding that both are likely constant stars based on current photometric data.

The value of professional-amateur collaboration was underscored by Miguel Rodríguez, who described the joint effort that enabled precise measurement of the orbital period of the old nova QZ Aurigae before and after its eruption—a result recently published in MNRAS.

The meeting also featured practical workshops on using GAIA data, time series analysis techniques, and new communication tools for the GEOS community, alongside opportunities for networking and visits to local astronomical facilities.

This event highlighted the vitality of the partnership between professional and amateur astronomers and reaffirmed GEOS’s commitment to advancing research and outreach in the field of variable star astronomy.

Conference Program

See the complete Programme (PDF)

Conference Abstracts

Laurent Corp: "AAVSO-Charts software"

In order to establish photometric measurements of the variable stars it is necessary to recover the field map as well as the magnitudes of the comparison stars.

Currently this operation is done manually by querying the website of the AAVSO (American Association of Variable Star Observers) and requires a lot of time.
In order to simplify the tedious manipulations I created a software that allows to download instantly the field map and the photometric data of a star or a series of stars.

The aim of this presentation will be to present the software and the results obtained.

Juan Fabregat: "Long term variability in Be stars, the scientific objectives of the GEOS prioritary"

Be stars are main sequence stars of B spectral type whose spectra present emission lines, originated by the reprocessing of photospheric radiation in an outflowing gaseous disc fed by mass ejected from the central star.

Be stars present photometric and spectroscopic variability in several time scales. In particular, many Be stars display long term quasi-periodic photometric variability due to variations in the size and density of the circumstellar disc, or outbursting activity attributed to episodic mass ejection from the photosphere. The amplitude of these variations make them accesible to visual observations.

The GEOS priority programme on Be stars aims to the monitoring of the irregular variations and to the detection of outbursting activity in a sample of bright Be stars, in order to contribute to the understanding of these phenomena and to facilitate follow-up observations.

Juan Fabregat: "OT Gem, revisiting the history of the old GEOS results"

The bright Be star OT Gem was very actively observed by the GEOS in the period 1977-1982. GEOS data allowed the detection of a bright outburst, the first ever observed for this star. In addition, the GEOS visual observations also detected the presence of periodic short term (3 hours), low amplitude variability, similar to the variability of beta Cep stars, which at that time was never been observed in a Be star. However, follow-up photoelectric photometry failed in detecting this short term variability, which consequently was considered as spurious.

In this talk I will re-analyse the GEOS result at the light of the current knowledge on non-radial pulsations in Be stars, present a new interpretation and propose new prospective observations.

Stéphane Ferrand: "RY UMi"

RY UMi is an understudied red star catalogued in GCVS as LB: 10.8-11.5 P Sp. M2. An intense 800 day survey by visual means led to highlight semi-periodic variations on a time-scale of 6 decades and a total range of 0.9 mag. Other contemporary measures clearly confirm the visual results.

J.F. Le Borgne: "RR Lyr stars candidates NSV 14264 and NSV 14172"

NSV 14264 and NSV 14172 are stars suspected to be variable stars of RR Lyr type. They were observed during three nights in October 2018 with a 25cm diameter telescope. These observations completed by ASAS-SN survey data bring to the conclusion that these two stars are not RR Lyraes but constant stars in the limit of the precision of the present photometry.

Other stars in the eld were also measured: known variable stars and stars not yet cataloged as variable are studied.

Raymonde Mat: VV Cep

What are the reasons which can explain why the parameters of that eclipse are so hard to define.

Miguel Rodríguez: "A professional-amateur collaboration studying old nova QZ Aur"

Last april, 25th, a paper entitled ‘Precise Measures of Orbital Period, Before and After Nova Eruption for QZ Aurigae’ was accepted in MNRAS. It comprises an historical series of magnitude measures from 1912 to 2016 and make an analysis of data which make possible a period measurement of binary system before and after nova explosion. A decreasing period is found, which have implications for cataclysmic variables evolution. Some of the observers who made QZ Aur measures (including myself) are included as co-authors.