BAA/AAVSO VARIABLE STAR MEETING – SATURDAY 7TH JULY

 

10.45 – 12.45 BAA/AAVSO Variable Star Meeting session 1

 

10.45 – 11.30 Dr Dirk Froebrich (University of Kent) The HOYS-CAPS Citizen Science Project

 

The talk will introduce the science goals of the HOYS-CAPS citizen science project and explain how to participate. We will also show some of the initial results.

 

 

11.30 – 11.50 Mike Poxon (AAVSO) Recent activity of SU Aurigae

 

Observations of the recent anomalous behaviour of the T Tauri star SU Aurigae are used in conjunction with previous studies to better understand the system.

 

 

11.50 – 12.10 Andrew Wilson (BAAVSS) Observational Evidence for Starspots on T Tauri Stars

 

Colour-Magnitude Diagrams (CMD) of young star clusters show a spread that is indicative of a spread in age. However, it could be that the stars formed at around the same time but a physical property of the stars is at least partially responsible for the spread. One such property is magnetic field of the Young Stellar Object (YSO). A strong magnetic field would inhibit convection, slowing contraction of the YSO towards the main sequence and thus causing a spread in the CMD. Starspots are a good indicator of stellar magnetic field. Spectra of T Tauri stars in the Orion Nebula Cluster and the sigma Orionis Cluster are being analysed to discover if they show the presence of a large surface covering by starspots. This work is being undertaken as part of Andrew’s PhD project at the University of Exeter under the supervision of Prof Tim Naylor.

 

 

12.10 – 12.30 John Toone (BAAVSS) The Discovery of TT Crateris

 

The discovery of TT Crateris was a remarkable achievement by an amateur astronomer. Visual discoveries of dwarf novae are rare and this one at the time of the Comet Halley apparition in 1986 was much fainter than the others that were found by professional astronomers during the period 1855-1904. This presentation explains the circumstances of the discovery and the follow-up efforts by amateur astronomers to obtain its official recognition in 1989.

 

 

14.00 – 14.50 Prof Tom Marsh (University of Warwick) AR Scorpii: a remarkable highly variable star discovered by Amateur astronomers

 

In May 2015, a group of amateur astronomers contacted Boris Gaensicke at Warwick regarding a puzzling star that they had been observing. This star, AR Sco, has turned out to be one of the most remarkable objects in the sky, unique for astonishingly strong pulsations every 2 minutes, and for radiating power across the electromagnetic spectrum, from radio to X-ray wavelengths.  I will describe what we think AR Sco is, how we arrived at this picture, and the extremely puzzling problems that it continues to pose.

 

 

14.50 – 15.10 David Boyd (BAAVSS) Long term orbital behaviour of eclipsing SW Sex stars

 

In 2006, encouraged by Boris Gaensicke, I began a long-term project to investigate the orbital behaviour of the 18 brightest eclipsing SW Sex stars. These are novalike CVs in which the high rate of mass transfer between the main sequence secondary star and the white dwarf primary via an accretion disc maintains the system in a persistent bright state. The initial aims of the project were to establish accurate ephemerides for these stars and to check if any of them deviated from a linear ephemeris. At the 100th Spring Meeting of the AAVSO in Boston in May 2011 I presented the results of the first 5 years of the project which combined new measurements of eclipse times with previously published observations. At that time, the majority of the stars appeared to be behaving consistently with linear ephemerides. However five stars indicated possible cyclical variation in their orbital periods and three more were clearly not following linear ephemerides. I now have a further 7 years of eclipse observations on these stars and it is time to revisit these earlier conclusions. It seems that linear ephemerides are no longer the most common option. Something is happening to upset the regular orbital behaviour in several of these systems.

 

 

15.10 – 15.30 Dr Franz-Josef Hambsch (VVS, AAVSO, BAV, GEOS) Seven years on the ROAD (Remote Observatory Atacama Desert)

 

After several tries at different places to set up a remote observatory, the ultimate destination has been found in San Pedro de Atacama at Alain Maury’s place called Spaceobs. Since its start on August, 1, 2011 the Remote Observatory Atacama Desert (ROAD) has produced tons of data due to the exceptional weather conditions in the Atacama dessert. The hard and software which is used is mostly off the shelf. A 40cm optimized Dall Kirkham (ODK) from Orion Optics, UK is the workhorse riding on a DDM85 direct drive mount from ASA (AstroSysteme Austria). The CCD is an ML16803 from FLI equipped with Astrodon UBVRI photometrical filters. Analysis of the images is done with the LesvePhotometry program written by Pierre de Ponthierre, an amateur astronomer from Lesve, Belgium. Further software packages in use are Maxim DL for image acquisition and CCDCommander for automatisation. From the start the focus was on pro-am collaborations and a few examples will be highlighted during the presentation. Most of the data are shared with VSNET in Kyoto, Japan, the Centre of Backyard Astrophysics (CBA), USA and several professional astronomers. Also most of those data are accessible from the AAVSO database (AAVSO user code: HMB). Related publications with co-authorship can be found on ARXIV using in the search box my last name.

 

 

15.30 – 16.00 Francois Teyssier (ARAS) Long term spectroscopic monitoring of the brightest symbiotic stars

 

Symbiotic stars are wide interacting binary systems comprising a cool giant and a hot compact star, mostly a white dwarf, accreting from the giant’s wind. Their orbital periods are hundreds of days (for S-type systems containing a normal giant). The accreting WD represents a strong source of ultraviolet radiation that ionizes a fraction of the wind from the giant and produces a rich emission spectrum.  They are strongly variable, according to orbital phase and activity and can produce various types of outbursts.  Symbiotic stars are considered as excellent laboratories for studying a variety of astrophysical problems, such as wind from red giants, accretion -eventually throw a disk-, thermonuclear outbursts under a wide range of conditions, collimation of stellar wind, formation of jets etc.

 

About 50 symbiotic stars in the galaxy are bright enough to be studied by amateur spectroscopy with small telescopes ranging from 8 to 24 inches.  We have undergone a long-term monitoring program in the visual range of the brightest symbiotics at a resolution from 500 to 15000. A part of this program is performed in collaboration with or upon the request of professional teams, feeding several publications at least partially (for instance: T CrB, AG Peg, AG Dra).

 

 

16.30 – 17.30 Prof Boris Gaensicke (University of Warwick) Gaia: Transforming Stellar Astronomy

 

The only way to measure the distances to stars is via a geometric parallax, making use of the fact that the Earth orbits the Sun. Over a century of work on ground-based parallaxes was limited in reach to a few 100pc, at best, and much of our understanding of stellar physics had to be based on proxy distance estimates. On April 25th, the ESA Gaia mission unleashed space-based astrometric data for over 1.3 billion sources, transforming stellar astrophysics over lunch time. I will illustrate the quantum leap in stellar astronomy  that these data enable, and will discuss how future large spectroscopic and photometric surveys will augment our understanding of stars both in quality and quantity.

 

 

BAA/AAVSO Variable Star Meeting – Sunday 8th July

 

09.00 – 09.30 Francois Cochard (Shelyak Instruments) Starting in Spectroscopy

 

Spectroscopy is more and more present in amateur astronomy, and gives deep physical information on the sky objects (stars, nebulae, novae & supernovae, comets...). We'll see how it works in real life: which equipment is required, the optical principles, how to run an observation. I'll also give you some key advice to successfully start in spectroscopy.

 

 

09.30 – 09.50 Robin Leadbeater (BAAVSS) Pushing the limits using commercial spectrographs

 

Some observations which explore the capabilities of three popular spectrograph designs

1. Simultaneous multi-band photometry of fast transients using a Star Analyser grating

2. Confirming and classifying magnitude 17 supernovae using an modified ALPY spectrograph

3.  Sub km/sec precision radial velocity measurement using a LHIRES III spectrograph

 

 

09.50 – 10.10 Andrew Smith (BAA) Towards full automation of high resolution spectroscopy

 

Following the successful automation of low resolution spectroscopy with a 300mm F5.4 Newtonian and a LISA spectrograph I decided to move to medium / high resolution with a 400mm ODK and homemade fibre-fed spectrographs R ~ 10,000 / 20,000.

 

This talk discusses the construction of the Medium Resolution echelle spectrograph (R ~ 10,000) and the work necessary to automate its operation to the point where I can supply it with target information, press “Run” on my Python program and retreat to the comfort of my arm chair.

 

The R ~ 10,000 echelle spectrograph is intended for accurate radial velocity measurement and to this end is temperature stabilised to better than +/- 0.04 degrees. It used a conventional layout with a R2 echelle and a F2 prism as cross disperser. Both the collimator and camera lenses are commercial camera lenses.

 

The route to automation rests on the core capabilities and script-ability of  Software Bisque’s The Sky X and the accuracy of the Paramount ME II. However, there are a number of challenges due to the small field of view provided by the Shelyak Instruments Fibre Guide-head at the 2.7m focal length of the 400mm ODK and the need to centre and maintain the target on a 75 micron hole. The separation of the finding and guiding tasks by using a dichroic beam splitter is central to the solution.

 

 

10.10 – 10.30 Gordon Myers & Ken Menzies (AAVSO) Applying Transformation & Extinction to Magnitude Estimates - How much does it improve results?

 

Photometrists regularly ask the question as to whether they should apply transformation and extinction corrections to their magnitude estimates. How much do these corrections improve the accuracy of their reported standard magnitudes? How much effort is involved in making these corrections? We quantify the significance of these corrections based on the characteristics of equipment (e.g., filter, CCD and field of view) and the conditions of the observation (e.g., airmass). Specific examples are presented for both CCD and DSLR systems.

We discuss the best practices that one should follow to improve their reported magnitudes and the AAVSO tools (VPhot, Transform Generator; Transform Applier) that facilitate an easy correction to your results. It is found that magnitude corrections for CCD observers are small but significant for most amateur equipment, and critical for most DSLR observers.

 

 

11.00 – 11.50 Dr Guillem Anglada Escude (Queen Mary, University of London) Red Dots Initiative: science and opportunities in finding planets around the nearest red-dwarfs

 

Nearby red dwarf stars are ideal grounds to search for small planets. The Pale Red dot campaign (2016) consisted in continuously monitoring of Proxima Centauri with the HARPS spectrometer. These campaign was aimed as measuring the motion of the star caused by a planet orbiting it using the Doppler effect. Although this is a mature technique to find planets, we are at the level where stellar activity contaminates the Doppler measurements and it is at the same level of the planetary signals under investigation. For this reason, additional information needs to be collected from the star. In particular, quasi-simultaneous photometric observations to the Doppler measurements are very useful to distinguish certain kinds of spurious signals from true planets. In 2017 we performed a second campaign called Red Dots where three more very nearby red-dwarfs were monitored spectroscopically and photometrically over 3 months. Many of the photometric observations were contributed by several pro-am astronomers with moderate size telescopes (~0.4m apertures), which are ideal for this kind of observations. I will review the status of the project, and discuss further opportunities for pro-am astronomer to contribute to this science case.

 

 

11.50 – 12.10 Lukasz Wyrzykowski (University of Warsaw) How to find planets and black holes with microlensing events

 

As shown by gravitational wave detections, galaxies harbour an unknown population of black holes at high masses. In our Galaxy, dark objects like black holes or planets, can be found and studied solely via gravitational microlensing, when a distant source star gets magnified by the space-time curvature caused by the lensing object. In order to measure the mass of the lens, hence to recognise black hole or a planet, it is necessary to combine highly sampled photometry from the ground with high accuracy astrometric data from Gaia. Well-coordinated observing effort, as in case of Gaia16aye binary microlensing event, will lead to full characterisation and discovery of a population of planets and black holes in the spiral arms of the Milky Way.

 

 

12.10 – 12.30 George Faillace D. Pulley, D. Smith, A. Watkins, and S. von Harrach, (BAAVSS) Short period eclipsing sdB binaries and the claims for circumbinary objects

 

It is well known that two orbiting objects do so around a common centre of gravity, or barycentre. What is less well appreciated is that this forms the basis of a powerful astrophysical binary star research tool of which amateurs can make use of as much as their professional colleagues. Our group used this technique to investigate if seemingly periodic variations in the position of the barycentre of seven short period (typically 2-3 hrs) sub-dwarf (sdBs) eclipsing binary systems, could indicate the presence of circumbinary objects: planets or brown dwarfs.  Following our 246 new observations made between 2013 September and 2017 July using a worldwide network of telescopes, we found that some systems showed possible cyclical variation over the short term, but did not follow predictions.  Only observations made over a very long timescale can resolve this and this is where amateur astronomers can make a significant scientific contribution.

 

Full details our paper entitled: “The quest for stable circumbinary companions to post-common envelope sdB eclipsing binaries? Does the observational evidence support their existence?” can be found in the  March 2018 Astronomy &Astrophysics Journal freely available via the arXiv portal  (https://arxiv.org/abs/1711.03749).

 

 

12.30 – 12.50 Geoff Chaplin (BAAVSS) RZ Cas: light curve and orbital period variations

 

Recent electronic observations have shown that amateurs can obtain very high quality data from modest equipment. This talk shows several such observations and shows how they can be used to determine the type of eclipse, re-evaluate historical visual data, calculate accuracy of times of minimum eclipse, and looks at the variation of the period and possible causes.

 

 

12.50 – 13.10 Kristine Larsen (AAVSO) Williamina Paton Fleming’s “Un-named” Variables and the AAVSO: A Scientific and Historical Perspective

 

Twenty years ago a JAAVSO article by Dorrit Hoffleit brought attention to the fact that fourteen of the nearly 300 variables discovered by Williamina Paton Fleming or her team at the Harvard College Observatory circa 1900 lacked permanent designations in the General Catalog of Variable Stars (GCVS). Most of these stars have now received such designations. Since their discovery, much has changed in our understanding of these variables. An exploration of this evolution provides a valuable series of snapshots in time of the state of variable star astronomy over more than a century, and illustrates the ongoing and significant impact of the AAVSO and its observers on the field.

 

 

14.00 – 14.50 Prof Christian Knigge (University of Southampton) Cataclysmic Variables as Universal Accretion Laboratories

 

Cataclysmic variables (CVs) are numerous, bright and nearby, making them excellent laboratories for the study of accretion physics. Since their accretion flows are unaffected by relativistic effects or ultra-strong magnetic fields, they provide a crucial "control" group for efforts to understand more complex/compact systems, such as accreting neutron stars (NSs) and black holes (BHs). I will review recent work on CVs, which has revealed that these superficially simple systems actually exhibit the full range of accretion-related phenomenology seen in accreting NSs and BHs. Given this rich set of shared behaviour, it is reasonable to hope that much of accretion physics is universal. CVs hold great promise in this context as observational testing grounds for attempts to model and understand this physics.

 

 

14.50 - 15.10 Dr. Thomas Morris (Oxford University) SN1987A and connections to Red Novae

I present a binary merger model for the progenitor of Supernova 1987A.  A binary system initially consisting of 15 and 5 solar mass stars in a wide orbit, which merges some 20,000 years before core collapse, is able to explain many of the unexpected features of SN1987A.
The common envelope phase gives rise to nova-like outbursts as primarily orbital energy is radiated from the common envelope. Such an outburst may explain the eruptions of V838 Mon, V1309 Sco and perhaps the 1840s outburst of eta Carinae. The 2001 to 2007 lightcurve of V1309 Sco observed by the OGLE project provides strong evidence for a merging binary within a common envelope.
 

 

15.10 – 15.30 Des Loughney (BAAVSS) rho Cas - an update

 

Rho Cas has been monitored by the author using DSLR photometry over the period 2007 to 2018 and the measurements are continuing,

 

Following the outburst and fade in 2001/2002, which was thought to happen every 50 years or so, it was expected that the star would revert to its standard pattern of semi regular variations. The measurements between 2007 and 2013 seemed to confirm this. The star varied semi-regularly between 4.5 and 4.9 magnitudes.  In 2013 an event occurred which heralded a new pattern of behaviour. The star brightened to 4.3 and faded to 5 magnitude.  A different pattern emerged which continued to 2018 when there was another mini outburst when the star brightened to 4.2. The brightenings, which are usually explained by mass ejections, are occurring more often and suggest that the dynamics of the star have changed.

 

 

15.30 – 15.50 Dr. Mario Motta (AAVSO) American Medical Association statement on street lighting

 

The American Medical Association (AMA) has adopted an official policy statement about street lighting: use low blue LED’s. I am the principle author. I will show my presentation that I gave to the Illuminating Engineering Society (IES), who make the streetlight standards in the USA, and hope for change in their recommendations soon.     

 

The LED street lighting that the industry had originally proposed and still suggesting is too harsh and bright for optimum safety and health. This report was adopted unanimously by the AMA House of Delegates at its annual meeting in 2016.  It states that outdoor lighting at night, particularly street lighting, should have a color temperature (CT) of no greater than 3000K.  Higher CT (4000K) generally means greater blue content, and the whiter the light appears.  

 

A white LED at CT 4000K contains a high level (over 30%) of short wavelength, blue light. These overly blue harsh lights are damaging to the environment and have adverse human health effects.  In some locations where they were installed, such as the city of Davis, California residents demanded a complete replacement of these high CT street lights for lower CCT lighting. Cities that have followed the AMA recommendations and adopted 3000K or 2700K, have seen much greater acceptance of LED lighting, and with much lower blue content which is better for human and environmental health, and reduces glare and thus safer for driving.

 

The AMA has made three recommendations in its policy statement:

First, the AMA supports a “proper conversion to community based Light Emitting Diode (LED) lighting, which reduces energy consumption and decreases the use of fossil fuels.”

Second, the AMA “encourage[s] minimizing and controlling blue-rich environmental lighting by using the lowest emission of blue light possible to reduce glare.”

Third, the AMA “encourage[s] the use of 3000K or lower lighting for outdoor installations such as roadways. All LED lighting should be properly shielded to minimize glare and detrimental human and environmental effects, and consideration should be given to utilize the ability of LED lighting to be dimmed for off-peak time periods.”