109th Annual Meeting
(In order of presentation schedule)
Keynote: Paula Szkody
Title: GW Lib and V386 Ser: CVs cont ainin g Accret ing, Pulsating White Dwarfs
There are now 18 cataclysmic variables in which the white dwarf is known to be pulsating. This provides a unique opportunity to monitor the inte1ior of the white dwarf when a dwarf nova outburst occurs and heats the white dwai'f. Theory predicts the pulsations should stop when the white dwarf moves out of its instability strip, and then resume at shorter pulsation periods which gradually grow as the white dwai-f cools back to quiescence. We have tested this the01y with optical and UV data on GW Lib and V386 Ser and find strange behavior in GW Lib while V386 Ser appeai·s to follow the theo1y so far. AAVSO data contributed to both these projects and we encourage further monit01i ng until these systems return to quiescence.
Presenter: Aarran Shaw
Title: Measuring the masses of white dwarfs with X-rays: A NuSTAR Legacy survey
Magnetic cataclysmic variables are binary systems consisting of a white dwarf accreting matter from a normal, Sun-like star. The magnetic field of the white dwarf is strong enough to distrupt the accretion flow, forcing material along the magnetic field lines on to the poles of the dense star, where it forms an extremely hot shock just above its surface. The temperature of this shock is directly related to the white dwarf mass, and can be measured by studying the hard X-ray spectrum. This method is complimentary to optical radial velocity measurements, which depend on the (often not very well-known) binary inclination.
With the 2012 launch of NASA's NuS1 AR X-ray telescope, the hard X-ray spectrum has become much more accessible to astronomers. We present here the results from a NuSTAR Legacy survey of 19 magnetic cataclysmic variables, measuring their spectra and deriving the masses of their white dwarfs. We present the mass distribution and draw comparisons with the masses of other classes of white dwarfs, commenting on the consequences our results may have on theories of accretion and novae in CVs.
Presenter: Gregory Sivakoff
Title: The Quick and the Deadtime
In an ideal world, we could image sizescales as small as the distance between the Earth and the Moon. However, even the highest resolution astronomical imaging facililities, like the Event Horizon Telescope, could only do so out to distances less than 100 parsecs (326 light-years) from Earth. However, since light travels from the Earth to the Moon in about 1.3 seconds, rapid variability can probe small distances across the entire Universe ... if your source is bright enough and you have a good setup. I will discuss recent rapid-variability results from relativistic jets launched by stellar-mass black holes that are feasting on the envelope of nearby stars. These results demonstrate the power (and pitfalls) of rapid variability (milliseconds to minutes). I will also discuss some of the equipment that astronomers are using to make such measurements ... especially CMOS/sCMOS detectors whose useful features include minimized deadtime due to quick readout, low readout noise, and windowing.
Presenter: Tom Richards
Title: Researching Eclipsing Binaries "Down Under": Illustrating the Methods and Res ults of Variable Stars South
Southern skies teem with variables but there are relatively few research-oriented amateur astronomers to study them; so a centralised funded research organisation is not rea listic. Instead, Variable Stars South (RASNZ) provides a very successfu l, virtua l non-localised base for scattered southern variable star researchers to collaborate in a project-oriented manner without central services.
This presentation illustrates that distributed but collaborative enterprise - rather different from the AAVSO model - by describing the very active work of the VSS's Southern Eclipsing Binaries Project. It shows how each observer carries out their own data analysis on their light curves, and how cloud collaboration is used to automatically combine their analyses and derive further results from them.
The presentation also shows with examples how that data is used by observers as the basis for more advanced research where again, individuals collaborate rather than using a central service. The approach has proved to be very productive over the seven years of the project.
Presenter: Filipp Romanov
Title: Discoveries of Variable Stars by Amateur Astronomers Using Data Mining: On the Example of Eclipsing Binary Romanov V20
Abstract: I report my discovery of high-amplitude Algol-type eclipsing variable star in the constellation Centaurus which was registered in the AAVSO VSX on December 3, 2018 under the name of Romanov V20. I describe the process of my analysis of data from VizieR catalogues to select this star as a candidate for searching for variability and to check if the variability of the star was known before; I inform how I used photometry data from several sky surveys to find variability, and how I researched this data in VStar software for light curve analysis and for period search. I explain about registering variable star in the VSX, about my requesting from the AAVSO a chart with comparison stars magnitudes and about my follow-up observations of the primary eclipse of this enough bright star with a remote telescope in Australia. I produce photometric measurements of Romanov V20 from these images and compare with data from sky surveys, and using this variable star as an example, I show that amateur astronomers can make astronomical discoveries and can conduct scientific research even without astronomical equipment, regardless of geographic location. Besides this variable star, I am currently the discoverer of 70 more variable stars, which have also been registered in the VSX since January 2016.
Presenter: Matthew Knote
Title: Characterizing the O’Connell Effect in Kepler Eclipsing Binaries
Abstract: The O'Connell effect – the presence of unequal maxima in eclipsing binary light curves – is a poorly understood phenomenon that has been recognized for over a century. Several ideas have been proposed to explain it, including chromospheric spots, effects of mass transfer, or circumstellar material, but the exact cause of the effect nevertheless remains unresolved. The Kepler mission observed nearly 3,000 eclipsing binaries, of which my analysis shows that over 200 show a significant O'Connell effect. Our goal is to analyze and characterize this sample of systems as a prelude to future projects looking to determine the physical cause of the phenomenon. I now present the results we have obtained thus far such as a correlation between the O’Connell effect size and eclipse depth. I will also discuss some interesting classes of systems we have discovered, including systems with considerable temporal variation and systems with asymmetric minima that warrant further observations.
Presenter: Todd Duncan
Title: Building a Connection through Community-based Astronomy
Abstract: Looking at the night sky can help us feel more connected to our fellow humans—perhaps because it reminds us what we have in common is far greater than our differences. In addition, the process of doing astronomy research can help us feel more connected to the larger universe. This presentation will summarize what we've learned by combining the two: bringing astronomy research (in the form of variable star photometry) out into public spaces to invite conversation and participation from anyone who happens to walk by our portable observatory.
Presenter: Donald Smith and Deshawn Reid
Title: Automating a Small Urban College Observatory
We will report on our efforts to automate the operation and data processing of the 16" RCOS optical telescope at the Guilford College J. Donald Cline Observat01y in Green sboro. NC. We will briefly describe the hardware and software that comprises the instrnment, and we will outline the Python scripts we have written to automate the observing schedule at night and the data reduction the next day. The final product is an ever-growing database of timestamped photometric measurements, from which can be easily extracted light cmves for analysis. This fall, we have been can-ying out our first observing campaign on several variable stars identified through the AAVSO Target Tool as needing further obse.iv ation s. We will present our prelimina1y light curves and discuss the precision of the analysis, including the effects of the local light pollution conditions.
Presenter: John Menke
Title: Using Bespoke 18 inch Newtonian and R=3000 Spectrometer for High Precision Observations
It is quite possible to make high precision spectroscopic measurements using rather modest (home-built) equipment. This paper describes a multi-year research effort on AZCas: A binary eclipsing variable with a 9 year period that has giant red and blue components. The next eclipse is in 2022 when previous observations show that we can expect substantial stellar interactions between the components. There are limited data on the system, including substantial uncertainty of the doppler shifts involved. Preliminary results give hope that doppler shifts can be measured to better than 0.1A (about 10km/s) even with a spectrometer resolution of about 2A.
Presenter: Helena Richie
Title: Disk Instabilities Caused the 2018 Outburst of AG Draconis
The symbiotic binary AG Draconic (AG Dra) has a well-established outburst behavior based on an extensive observational histroy. Usually, the system undergoes a 9- to 15-year period of quiescence with a contant average energy emitted, during which the system's orbital period of ~550 d can be seen at shorter wavelengths (particularly in the U-band) as well as a shorter period of ~355 d thought to be due to pulsations of the cool component. After a quiescent period, the marker of an active period is usually a major (cool) outburst of up to V = 8.4 mag, followed by a series of minor (hot) outbursts repeating at a period of approximately 1 year. However, in 2016 April after a 9-year period of quiescence, AG Dra exhibited unusual behavior: it began an active phase with a minor outburst followed by two more minor outbursts repeating at an interval of ~1 year. We present R-band observations of AG Dra's 2018 April minor outburst and an analysis of the outburst mechanism and repeorts on the system's activity levels following the time of its next expected outburst. By considering the brightening and cooling times, the scale of the outburst, and its temperature evolution we have determined that this outburst was of disk instability in nature.
Presenter: Madelyn Madsen
Ttitle: Simultaneous photometry on VSX variables and TESS exoplanet candidates
As a continuation of our software development as part of the TESS ground-based follow-up network, we have been able to produce the data products necessary for a TESS submission. Currently we are able to produce a photometry measurement table, light curve, seeing profile, a field of labeled apertures, and corresponding measurement files. We have made one successful submission to TESS, and we are now working on streamlining the analysis process for other submissions. We are also able to measure the photometry of variable stars in the field and have observed a possible new variable in the field we submitted to TESS.
Presenter: Joyce A. Guzik
Title: Search for Variability in 30 Bright Metallic-line Stars Observed by the TESS Spacecraft
As part of the NASA TESS Guest Investigator Cycle 2 program, we received 2- minute cadence light curves for bright main-sequence metallic-line A (Am) stars. The Am stars show significant underabundances of calcium and scandium, and enhanced abundances of titanium and iron-group elements compared to the solar abundances. Catanzaro et al. (2019) used high resolution spectroscopy + Gaia parallaxes to derive a set of uniformly reduced parameters for these stars, including log g, v sin i, effective temperature, luminosity, and element abundances. While these stars lie in or near the delta Scuti pulsation instability region in the H-R diagram, they are not expected to pulsate because the diffusive element settling and radiative levitation processes responsible for their peculiar abundances should have also drained helium from the layer in the envelope that drives delta Scuti pulsations. Of the 30 stars observed by TESS, we find four delta Sct stars, two of which may be delta Sct/gamma Dor hybrids. Of the remaining stars, we find one previously known eclipsing binary, and 16 showing variability of unconfirmed origin. We will show example light curve analyses for a delta Scuti star, for one of the higher amplitude variables, and for the eclipsing binary. Follow-up observations combined with stellar modeling will be needed to understand the causes for the variability.
Presenters: Richard Berry, Nolan Sottoway, and Sol McCain
Title: New Observations of the SX Phe star XX Cygni
We report 20+ new tim es of maximum light of the short period pulsator XX Cygni measured dur ing the August 2020 Pine M ounta in Observatory " Virt ual Astronomy Camp" for high-school st udent s. Observations were made at a cadence of 10 seconds, producing dense light curves. We determined each time-of-max by fit ting N250 data points near the peak with a six-order polynomial. Assuming a constant period for the star, the standard error from the ephemeris is 0.00025 days = 22 seconds. We saw no evidence for early or late tim es-of-max dur ing our observing campaign.
Presenters: Dr. Pradip Karmakar, Horace A. Smith, and Wayne Osborn
Title: Types of Period Changes of W Virginis Stars
There are still unsolved problems in understanding the evolution of type II Cepheids of the W Virginis class. Period changes of W Vir variables have the potential to provide insight into that evolution. We illustrate this by showing the observed period changes of three W Vir variables in globular clusters. V2 in M10 shows a long-term decrease in period. V3 in M10 shows a small period increase. Sometimes, as with V1 in M12, irregular period changes make it hard to determine the long-term trend of the period change.