AAVSO 2022 Annual Meeting Abstracts

Sean Walker will share the story of the development and current progress of the MDW Sky Survey, an all-sky mapping project undertaken by a trio of New England amateurs, including David Mittelman and Dennis di Cicco, using a pair of remotely operated telescopes currently situated at the New Mexico Skies facility in Mayhill, New Mexico. Sean will detail how the survey operates, several discoveries the team has contributed to, and its upcoming plans to publicly release the data in partnership with Columbia University and the Mittelman Family Foundation.

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The AAVSO Photometric All-Sky Survey (APASS)

Dr. Henden will be discussing special elements of the AAVSO Photometric All-Sky Survey (APASS). APASS was started from discussions with Arlo Landolt, and was awarded an NSF grant based on his support of the project. All-sky calibration is necessary for the AAVSO to provide comparison stars for targets of interest, and APASS was designed to meet that goal.  Arne will highlight the early history of the all-sky calibration project, as well as comparisons with other surveys. He will also announce the status of DR11, the next formal release of APASS. Dr. Henden will then conclude by describing the new XPASS and APASS2 projects, with their all-sky completion and bright-star extension, along with volunteer opportunities for helping with the survey.

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A Program for Characterizing Variable Stars Discovered in the MOTESS-GNAT Sky Surveys

Eric R. Craine, Western Research Company, Inc. and GNAT, Inc.

Brian L. Craine, Western Research Company, Inc. and GNAT, Inc.

Roger. B. Culver, Prof. Emeritus, Colorado State University and GNAT, Inc.

The motivation of this project is two-fold: 1) to help provide quality control over a large, new database of astronomical observations, and 2) to explore details of select, interesting variable stars not previously well characterized.  The Moving Object and Transient Event Search System (MOTESS) and Global Network of Astronomical Telescopes (GNAT) projects have collaborated from 2001 to 2021 to conduct time series photometric surveys of selected strips of sky along the celestial equator. This project has yielded several million stellar light curves among which are many thousands of newly discovered or previously uncharacterized variable stars. 

The problem being addressed is to understand nuances of the databases and to provide in-depth analyses of particularly interesting stars within the databases. The methodology is to recruit observers to collaborate with the GNAT research teams to observe, analyze, and publish results for MG Sky Survey stars of interest.  The requisite follow-up observations are predominantly small telescope time series photometry and large telescope spectroscopy.  The former in particular is a rich area for participation by serious amateur astronomers who are equipped for such photometry in the 14 < R < 18 mag range.  A goal of this presentation is to encourage such observers to productively join our research teams and to share in authorship of the final results. 

This presentation will provide some examples of the results to date of this program, including a summary survey of the properties of the MG Sky Surveys, and discovery papers of interesting survey variable stars: a new sample of M-dwarf eclipsing binary stars, previously unknown long period variables, dynamic systems characterized by extremely high-energy outbursts, and others. These results are of value in paving the way for publication of the survey data as well as furthering our knowledge of the extremes of behavior of different classes of variable stars.

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A CubeSat for UV/Optical Pro-Am Astronomy

Douglas Walker, Prime Solutions Group, Inc.

Kevin France, Department of Astrophysical and Planetary Sciences, University of Colorado

John Martin, Department of Astronomy – Physics, University of Illinois 

Ken Spencer, Astronomy Association of Arizona 

Dirk Terrell, Department of Space Studies, Southwest Research Institute 

Prime Solutions Group, Inc. (PSG) in partnerships with Southwest Research Institute (SwRI), the University of Colorado at Boulder, the University of Illinois, and the Astronomy Association of Arizona (AAA) are proposing the development, launch, and operation of a UV/optical CubeSat mission for stellar astronomy.

The scientific motivation for a general UV observatory includes the following:

• The UV portion of astronomy research reveals a wealth of information about hot and energetic processes in astronomical objects.
• Time domain UV astronomy has not been studied extensively (Sagiv et al. 2014; Mathew et al. 2018)
• Only a few current large space missions, HST and Gaia, cover the UV spectral range and are mission shared.
• The UV sky background is faint, making a majority of variable sources detectable with a small space-based observatory (Safonova et al. 2013)
• Scientific community will soon be entering a period without any continuous orbital UV coverage.
• This project helps fill a critical need in the observational UV astronomy gap until NASA’s Large UV/Optical/IR Surveyor (LUVOIR) is brought online 2040?

The system objectives for such a mission will include:

• Provide a general UV/optical imaging system which is widely available for scientific, educational, and amateur utilization.
• Help fill the UV imaging gap between 2025 and 2040.

The scientific objectives are:

• Stellar/galactic
  • Bright transient sources (supernovae) (Welsh et al. 2011; Wils et al. 2010; Ganot et al. 2016)
  • Active Galactic Nuclei (Wang et al. 2019)
  • Flare stars (Welsh et al. 2007)
  • Gravitational wave counterparts (Ridden-Harper et al. 2017)
• Solar System
  • Venus – observations help fill gaps between NASA missions (Limaye et al. 2018)
  • Pluto – observations of atmosphere via stellar occultations (Kammer et al. 2020)
  • Asteroids (Xing, Z., Bodewits, D. 2021)
  • Trans-Neptunian Objects (Tan et al. 2021)
• Exoplanets
  • Planetary eclipses
  • Atmospheric detections (Lopez et al. 2022)

And finally, the educational objectives for K-12 through the university level are:

K-12

• Provide exposure of spaceflight and astronomy to students
• Enable participation in aspects of the missions (reviewing imagery, suggesting targets, etc.) 

Community College/University Level

• Provide observational data to university faculty and professional astronomers to conduct original research in their areas of expertise
• Provide synergy between UV satellite data and ground-based data that is achievable with college and semi-professional observatories

General Public

• Provide observational data and guidance to amateur astronomers in order to conduct original research and publish their findings 

The stellar observatory mission will consist of a ground- and space-based UV/optical telescope system designated as the Ultraviolet Follow-on Observatory (UFO). This proposed CubeSat will be a 12U system housing a 125mm telescope and designed for a four-year plus mission timeline in high Earth orbit. A camera capturing simultaneous UV/optical observations will first be developed and tested on a ground-based telescope before being designed and integrated into the CubeSat. UFO will follow in the footsteps of the successful launch and operation of the Colorado Ultraviolet Transit Experiment (CUTE) and the planned launch of the Star-Planet Activity Research CubeSat (SPARCS), which are paving the way for this new era in CubeSat space-based astronomy. The operation of UFO (UV wavelength range of 240nm to 390nm (UVC, UVB, UVA) for space-based) will expand on these missions. This will demonstrate that small telescope observations in the ultraviolet frequency can provide valuable data to the astronomical science community and will help fill a critical need in the observational ultraviolet astronomy gap until NASA’s Large UV/Optical/IR Surveyor (LUVOIR) mission launches in the early 2040s timeframe.

Outreach Work by an AAVSO Ambassador

I really think it is important for me as an AAVSO Ambassador, to present about the outreach an ambassador is doing and to let people know different ways of promoting Astronomy as one’s favourite subject and AAVSO as an esteemed Organisation. I will show how an ambassador at the AAVSO is doing their work, why is outreach important, and what the final expectations that can be fulfilled are, i.e, getting people involved in astronomy and participating in AAVSO’s programs in many ways.

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Dynamic Methods for Transforming Photometric Observations to a Standard System

The advent of the CCD and other linear astronomical cameras has made it easy for amateur astronomers to obtain good and useful data about variable stars.  However, to make the most use of the data it is necessary to transform them into a standard photometric system to facilitate the accumulation of data from many observers.  AAVSO has made this easy with the Transform Generator.  This software is used to determine transformation coefficients that convert raw observations into a standard system.  

However, this method ignores second order extinction coefficients that are important for low altitude observations with high air mass.  Moreover, changes to the imaging system caused by modifications to the optical train, changing filters, the accumulation of dust, or other such variations can induce errors requiring the generation of new transformation coefficients.

This study explores several alternative means of estimating these coefficients using comparison stars in the target image.  Clearly, such coefficients will be using the most current setup of the imaging system so the focus of this study is to determine whether such (non-standard) comparison stars are accurate enough to produce good transformation coefficients.  This concern is mitigated by two factors: (1) as more data have been gathered, the magnitudes of the comparison stars of a given field have become more accurate, and (2) with the larger fields that are available with today’s cameras, there are more comparison stars, allowing for statistical variance reduction methods.  

The equipment used in this study was an Astro-Tech 10” f/8 RC scope with a SBIG ST-10XME camera supplied with Astrodon B and V filters.  Single binning was employed yielding an image scale of 0.701 arc second per pixel.  Twilight flats were generated for each night as were dark and bias frames.  Using the AAVSO Transform Generator, we estimated two sets of transforms using the standard fields in NGC 7990 and M67.  As both fields were quite crowded, we deleted any comparison star that overlapped with another, usually keeping the brighter star.  

We compared five different methods:  a “null” method with no TC applied, the standard TC method, two dynamic TC methods using comparison stars, and an all-sky fit of the basic coefficients including zero points, color coefficients, and first and second order extinction coefficients measured over one night’s imaging with air mass ranging between 1.06 to 2.29.  

The results showed a distinct improvement using dynamic coefficients over the standard TC’s in estimating check star magnitudes in images with high air masses using a B filter.  The performance with the V filter was not statistically significantly different for any method versus doing no transformation.  For low air masses, there was a small improvement using the dynamic coefficients.  The best performance occurred using the all-sky fit of the parameters, but this was using comparison stars in M67 (a standard field) to estimate check stars in the same cluster.  We also noted that for one field with few comparison stars, there was no statistical motivation (i.e., the regression was poor) to use any TC.  However, these comparison stars were around the same color as the check stars they were measuring so any TC would provide a very small correction.  

We conclude that dynamic transformation coefficients may be a better method, particularly for large fields with many, fairly accurate, comparison stars.  However, before that would be useful to the amateur, the available photometry software would need to be updated to (1) compute the dynamic coefficients, and (2) do a statistical study to determine if they are significant.  

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How to Select Comparison Stars and Why?

Photometrists regularly ask: How many comparison stars should I use and how should I select them? We evaluate several criteria that should be considered:

1. How many comps (one or ensemble)?
2. How close (location)?
3. What Color?
4. What Magnitude?
5. What Catalog?

We utilize images of two AAVSO Standard Fields to evaluate the precision (random error/noise) and accuracy (systematic error/bias) of magnitudes calculated for ten targets using one to ten comparison stars in 8-10 images in both B and V filters. VPhot was used to conduct differential photometry, apply ensemble photometry (1-10 comps) in a time series of 8-10 images, and/or apply transformation to reduce the data, and to compare the precision and accuracy of measured magnitudes versus Henden USNO Standards.

We address three major questions concerning how these criteria impact differential photometry: (1) Does precision improve when multiple comparison stars (single comp versus ensemble) are used for magnitude calculation, (2) Does accuracy improve when multiple comparison stars (single comp versus ensemble) are used, and (3) Does accuracy improve when magnitudes are color transformed to the standard system. 

We report the following results and observations: (1) AAVSO Standard Fields provide effective analysis of precision and accuracy of photometric systems, (2) VPhot and Excel Tools facilitate analysis, (3) Differences between Observed and Known Magnitudes (O-K) are statistically improved by careful selection of the comp(s) and/or transformation, (4) Precision of a time series does not differ whether using one or more comps despite what most software imply, (5) Multiple comps do not consistently improve the accuracy of the magnitude but using more comps does smooth the variation, (6) 3-5 comps may be adequate in improving the consistency of magnitude measurement, and (7) As expected, selection of proper Comp SNR, Photometric Aperture, and Image Quality impacts experimental error and bias. The typical random error achieved by amateur systems is 0.01-0.03 mag. The typical systematic error achieved by amateur systems is 0.01-0.5 mag depending on the selection of comparison stars and transformation coefficients.

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MWC349: Outburst or Anomalous Photometry?

The author has been intensely observing the enigmatic star, MWC 349, for the past year in five colors--VRI & H_a and H_ac from Sierra Remote Observatory.  On the nights of JD 2459793 and 2459794 (2022 August 1-2) the light curve showed quite unusual behavior in all colors.   The possibility of a discovery on the one hand, and many conversations regarding errors in the database with member Tom Calderwood on the other hand, led to an intense review of the photometry.  The result was the makings of an algorithm that can be used with time series data to "clean" the database and present the data in a form that may be more acceptable to our professional colleagues.  The author shares this algorithm methodology and hopes that this will lead to a modification of the AAVSO International Database (AID)  with the help of some software modifications to WebObs.  

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Arlo U Landolt (1935-2022): A Life Above Standards

To many professional and amateur astronomers, the name Arlo Landolt is commonly associated with standard stars. However, few realize that he made many other contributions to the astronomical community beyond “his” invaluable photometric standards, and even fewer got to experience the man as a mentor, colleague, and dear friend, as I did. I intend to honor the man (and the legend) by offering a personal perspective on his research career in the more recent years before his passing, and strive to convey how truly unique of a life he lived.

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Development of an observational astronomy course and accompanying open source software

An observational astronomy course has been offered at Minnesota State University Moorhead annually or semi-annually since 2011. Over that time we have taken a variety of approaches to image processing and data analysis. Though there are several software tools available, including MaxIm DL, AstroImageJ, AAVSO’s VPhot, and, more recently, EXOTIC, none of those tools span the full range of what we would like to do in the course: create a color image, measure and submit data of an exoplanet transit, and submit variable star data to the AAVSO. In addition, some present installation challenges, or are not free, and/or cannot be installed locally. The course needed to be offered online during the pandemic, which led to a substantial change in lecture structure, which also seems more effective in-person.

Since 2015, I’ve been developing Python-based software that attempts to perform more of the functions we need with less effort around installation and access. Several of these attempts can only be described as failures, though I believe we have settled on a solution – open source Python software running on a JupyterHub server on a University-run virtual machine – which entails less effort for the instructor and eases the student experience with the software. The same set of software can be installed on individual student computers if desired. One of the design goals is to allow easy integration with other software like AstroImageJ and EXOTIC. 

Students have submitted transit data to TESS and through EXOTIC from this software. The most challenging case to automate is submission to the AAVSO. Those challenges will be discussed, along with the potential for software along these lines to serve in the future as one way to analyze observations for submission to the AAVSO that can be run on a hosted server, like VPhot, or on an observer’s own computer. 

Links to installations instructions and to the lecture notes for the last two times the course was offered, and the notes for the Fall 2022 version will also be provided.

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A Glimpse into in a High School Astronomy Classroom

Education is an intensely discussed topic; however, most are far removed from the daily processes and experience of a working classroom. Take a glimpse into a high school astronomy classroom in Atlanta, Georgia, where students of all academic levels are introduced to a variety of astronomical topics, including spectroscopy.

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Reference Set of Mira Variables for the World to Share

Authors:  M. J. Creech-Eakman¹, G. van Belle², D. Baylis-Aguirre¹

Affiliations:  1 – New Mexico Institute of Mining and Technology, Physics Department

                       2 – Lowell Observatory

Our team has recently been awarded an NSF grant to create a Reference Set of Mira variables based on nearly a decade of optical interferometry observations undertaken with the Palomar Testbed Interferometer (PTI).  Miras are in some respects the most enigmatic regular pulsators, while also being potentially the most important galactic recycling factories, given their high-luminosities, period-luminosity relationships, complex circumstellar environments, and broad distribution throughout the galaxy.  The dataset from PTI contains almost 100 Miras periodically changing size during their year-long pulsations with resolutions at the submilliarcsecond level.  The dataset covers a full range of oxygen to carbon-rich chemistries and includes objects that are likely within about 2 kiloparsecs of the Sun, making them ideal for detailed studies of their atmospheres and mass-loss processes. Our team will supplement the PTI data with archival and contemporaneous data from missions/databases such as 2MASS, COBE, IRAS, Spitzer, SOFIA, TESS, WISE, and NRAO, as well as attempting to improve distance estimations with a novel approach using GAIA/Hipparcos data.  We will present a few examples of science that will be enabled using data on Miras from this set.  We will provide a list of all the Miras in the set for anyone who would like to add them to their observing programs.  All the data we produce and collate for this Reference Set will be hosted on a website open to the public so that other researchers and citizen scientists can participate in expanding the utility and body of knowledge on this set of “wonderful” stars.

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Characterizing Mass Loss in Mira and SR Variables in the LMC

Authors: Henry Prager, Lee Anne Willson, Michelle Creech-Eakman, Massimo Marengo, Joyce Guzik, Qian Wang

Asymptotic Giant Branch (AGB) stars, which make up the Mira variables and a substantial part of the semi-regular variable stars, have long been of interest to astronomers. These stars are in a crucial stage of stellar evolution, losing their mass and transitioning into planetary nebulae. Characterizing the long-term evolution of mass loss through a mass-loss formula in these stars has been elusive.
To try and get a firmer grasp on this problem, we analyzed a set of AGB stars in the Large Magellanic Cloud. Going in, we knew that a reasonable mass-loss formula should create a sharp turn in luminosity-mass space. That is, they should evolve at nearly constant mass, reach a critical zone near the right edge of the strip, transition smoothly to evolving at near constant luminosity, and then exit the bottom of the strip. Initially, we tried a linear fit of the luminosity and pulsation period to the mass-loss rates of the stars. This fit was clearly incorrect, leading us to attempt more complicated fitting methods which did not help us. We realized that the measurement errors of luminosity and mass-loss rate made standard fitting methods practically impossible as opposed to simply unreliable.
Noting this, we developed a method to determine a mass-loss formula by analyzing the distribution of stars in the pulsation period-luminosity plane. This method uses a program to `seek' a formula that minimizes the difference between measured and predicted mass-loss rates using the population's change in luminosity and pulsation period during stellar evolution. Through this, we found four mass-loss formulas for four different subsets of the AGB population. These formulas reproduce the sharp turn we expect from observations of AGB populations and from theoretical models, putting formulas from theory and observation into agreement.

As a next step, we are generating grids of atmospheric models of AGB stars to compare against the stars seen in the Large Magellanic Cloud. We will be examining how models with typical parameters compare, how they compare when these parameters are pushed to their expected limits, and investigating what details and physical processes might need to be accounted for to make these grids fit stars observed in the LMC.

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Outbursts in ultracompact white dwarf binaries: powerful tools to understand their interaction processes

Ultracompact white dwarf binaries, or AM CVns, have orbits of less than 70 min., and a fraction of that class of binaries shows outbursts. Until recently, instabilities in the accretion disk were commonly invoked to explain the origin of these accretion-related phenomena. In this talk, I will discuss how traditional models have been challenged, and how our understanding of outbursts in AM CVns has recently changed thanks to continuous photometric observations of the known systems with ground- and space-based telescopes. I will describe how observers everywhere can contribute to investigate these interacting binaries. I will also address the importance of considering additional mechanisms to disk instabilities in order to quantify their influence on AM CVn evolution, and the impact these mechanisms might have on the detection rate of AM CVns with upcoming photometric surveys and gravitational wave observatories.

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Comparison of the 3D Printed Spectroscopes LowSpec and StarEx: Design, Construction, and Performance

In this presentation, I will describe the two most popular homemade spectroscopes that are currently of interest within the amateur spectroscopy community.  I have built both of these devices and have operated them on my 8” SCT telescope.  My presentation will begin with a comparison of the design of each of the two spectroscopes.  The LowSpec was designed by the Dutch amateur astronomer  Paul Gerlach, who has provided for free all the needed files and construction instructions on the website “Thingiverse”.  The StarEx is a variation of the Solex spectroscope designed by the French spectroscopist Christian Buil, who originally intended it for solar observations.  His StarEx version includes a guide module making it appropriate for longer duration exposures and thus capable of recording the spectra of stars. Buil has extensive support information on his website and offers the 3D printing files for free.

The presentation will include an overview of the 3D printing process for each of the devices as well as comments on the practical issues relating to assembly and tuning.  Costs for both devices will be presented.  Then, the performance of the devices will be compared using spectra taken of the same targets with otherwise identical instrumentation.

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Measuring the Masses of Monster Black Holes

One of the lasting legacies of the Hubble Space Telescope is the discovery that every galaxy has a supermassive black hole lurking in its center. Furthermore, these black holes and their host galaxies seem to have a symbiotic relationship in which they grow and evolve together over cosmic time. One of the keys to understanding this relationship involves measuring the masses of the black holes, and thus, constraining the strength of their influence. However, weighing an invisible object in the center of a galaxy that is millions or billions of light years away is difficult. I will describe one of the main techniques that has been developed for this purpose over the last 30 years, reverberation mapping, in which light echoes are used to probe the hot gas in the gravitational field of an accreting supermassive black hole. I will also highlight the ways in which monitoring with broad-band photometry on small telescopes can particularly contribute to the advancement of knowledge in this area. Ultimately, the observational study of black holes allows us to develop a clearer picture of the formation and evolution of galaxies, including our own Milky Way, over the 13 billion year history of our universe.

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Transiting Exoplanet Science Results from Citizen Astronomers with the Global Unistellar Network

Thomas M. Esposito (1,2,3), Paul A. Dalba (4,1,5), Lauren Sgro (1), Amaury Perrocheau (1), Franck Marchis (1,2), Arin M. Avsar (6), Daniel O’Conner Peluso (1,7), and 170 Unistellar Citizen Scientists

1. SETI Institute, Carl Sagan Center, Mountain View, CA 94043, USA
2. Unistellar Corp., San Francisco, CA 94110, USA
3. Astronomy Department, University of California Berkeley, Berkeley, CA 94720, USA
4. Heising-Simons 51 Pegasi b Postdoctoral Fellow
5. Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
6. Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
7. Centre for Astrophysics, University of Southern Queensland, Toowoomba, QLD, Australia

Citizen astronomers in the Unistellar Network are contributing critical exoplanet transit observations from around the world to support groundbreaking missions with NASA’s TESS and the James Webb Space Telescope (JWST). Since April 2020, 170 different observers have produced over 1,000 transit observations and 250 detections of giant exoplanets using eVscopes (4.5-inch "Enhanced Vision Telescopes") in partnership with SETI Institute astronomers. At least 70 of these photometric time series data sets are publicly available in the AAVSO Exoplanet Database for additional studies by the community. We will present highlights of our exoplanet results, including early returns from a NASA-funded program aimed at confirming and refining orbits of long-period, long-duration planet candidates from TESS. We will also give an overview of the Unistellar Network, our citizen scientist community, the eVscope, and our observing and data processing strategies, along with our plans for the future of the network regarding exoplanets and our other science campaigns.

With >5,000 new exoplanet candidates recently discovered by NASA's TESS mission, and the need to identify prime giant planet targets for detailed characterization by current & future large missions, ground-based follow-up facilities are in high demand. Many of our targets are TESS candidates that require additional observations to confirm their planetary nature and/or refine measurements of their orbits. Even for confirmed planets, regular transit timing measurements make new observations by major telescopes, like JWST and the Ariel satellite, more efficient by increasing the precision of future transit predictions. This is especially important for long period planets (>100 days), which our network is particularly well-suited to observe with its broad geographical coverage and over 10,000 telescopes.

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Exoplanet Watch:  Inviting Citizen Scientists to Observe Transiting Exoplanets

Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA

Due to the efforts by numerous ground-based surveys and NASA’s Kepler and Transiting Exoplanet Survey Satellite (TESS), there will be hundreds, if not thousands, of transiting exoplanets ideal for atmospheric characterization via spectroscopy with large platforms such as James Webb Space Telescope and ARIEL. However their next predicted mid-transit time could become so increasingly uncertain over time that significant overhead would be required to ensure the detection of the entire transit. As a result, follow-up observations to characterize these exoplanetary atmospheres would require less-efficient use of an observatory’s time—which is an issue for large platforms where minimizing observing overheads is a necessity. Here we demonstrate the power of citizen scientists operating smaller observatories (<=1 m) to keep ephemerides “fresh,” defined here as when the 1σ uncertainty in the mid-transit time is less than half the transit duration. We announce here the launch of Exoplanet Watch, a community-wide effort to perform ephemeris maintenance on transiting exoplanets by citizen scientists for the professional exoplanet community. Based on >500 observations to date, we demonstrate the capabilities and results of Exoplanet Watch to calculate updated ephemerides, confirm planet candidates, spatially-resolve stellar blends, monitor for epoch-to-epoch stellar variability, and search for new planets or constrain the masses of known planets with transit timing variations greater than two minutes.

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No Longer Eclipsing—The Strange Case of RS Crateris

Ten years ago, the number of stars convincingly established to have stopped eclipsing numbered but six objects: QX Cas, SV Cen, SV Gem, SS Lac, AY Mus, and V907 Sco.  Recently, based on TESS observations, James Davenport et al. have added HS Hya to that list. I ask, “Should RS Crt be included?”  Based on eight minima from European and Soviet astronomers in the 1930-1944 era, RS Crt was listed in early GCVS editions as an Algol eclipsing binary (EA) with a 10.8 to 11.5 photographic magnitude range, period of 0.8168 day, and six-hour long eclipses.  But, lacking additional times of minima and armed with new ASAS data, in July 2021 AAVSO VSX administrator Sebastián Otero reclassified it. It’s now listed as constant at V mag 10.62 with no mention of its eclipsing binary past. Based on three things—the poor quality of the early data, the suspicious nearby presence of possible inappropriate comparison star X Crt, and reported eclipse duration too long for an EA—one could argue that RS Crt never was an eclipsing binary. 

I counter that argument by using data from the digitized Harvard Plate Collection (DASCH project) and presenting two new minima of RS Crt (in 1938 and 1944, consistent with published period and epoch).  And—in bolstering the hypothesis that its eclipses had stopped by the mid-1970s— I cite a 13-month long visual study of it (by Kurt Locher) reported in March 1976, 152 visual estimates (from Marvin Baldwin) spanning 32 nights between April 1987 and February 1989, and my own April 1995 differential photometry with small wide-angle lens, V filter, and ST6 CCD.  The latter showed no variation beyond 0.082 mag (standard deviation-based) scatter.

In 2020 I did better differential photometry—using a 130-mm F/5 reflector—and assembled 198 data points covering 13 nights between May 8 and June 15.  They show RS Crt to be constant with 0.042 V mag scatter. Discrete Fourier Transform-based analysis of this last data set failed to find evidence for the published period, nor did similar analysis of the 1987-1989 visual data—although its scatter was roughly four times larger.  

Three spectra and radial velocity data obtained at Lick Observatory by Dan Popper and reported in 1996 rule out the published short period for RS Crt, but not its possible binary system membership.  Its eclipses could have stopped as system orbital inclination changed, like V907 Sco and HS Hya, or after a stellar collision. Alternate (less likely?) explanations involving a pulsating star that ceased pulsating, or a fast-rotating star that slowed— and whose starspot-covered surface changed— can be advanced. More and better data are needed to decide. For now, eclipsing binary enthusiasts should keep watching. RS Crt could do what V907 Sco and HS Hya are predicted to do: begin eclipsing again, in 2030 and 2195, respectively.

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Double-Pulsator `Hidden’ Binaries: New Targets for Studying Classical and Solar-like Oscillations

The NASA Kepler space mission revolutionized the field of stellar astronomy through the discovery of thousands of classically pulsating A-F type stars and tens of thousands of main-sequence, sub-giant, and giant-branch stars with solar-like oscillations (Balona 2018; Hon et al. 2019).  Whereas solar-like oscillations display regular frequency patterns that can be used to determine stellar parameters (Brown et al. 1991; Kjeldsen and Bedding 1995; Kallinger et al. 2018), classical oscillations display more complex frequency patterns which can make mode identification difficult (Guzik 2021).  Studying stellar pulsators in binary star systems provides the unique opportunity to constrain stellar parameters in order to allow more detailed oscillation analysis (Streamer et al. 2018; Steindl et al. 2021).  Though eclipsing binaries provide the most direct path to identifying precise masses/radii for classical pulsators, the sample discovered by Kepler is small and biased towards short period, circular systems (Kirk et al. 2016).  Using spectroscopy for the detection of pulsator binary star systems not only increases the sample size of pulsating binaries, but also expands the sample to new regions of orbital parameter space, e.g. longer periods and more eccentric orbits (Beck et al. 2022). By using scaling relations in concert with the orbital and stellar constraints provided by a spectroscopic binary, `hidden', e.g. non-eclipsing, double-pulsator binaries that contain a solar-like oscillator and a classical oscillator allow for detailed analysis of classical pulsations (Murphy et al. 2021).

In order to take advantage of the high asteroseismic performance of Kepler data, potential double-pulsator `hidden’ binary targets were drawn from a sample of identified Kepler red giants.  Gaulme et al. (2020) flagged the power spectral density (PSD) of 21 Kepler red giant time series as displaying signatures of classical oscillations in addition to red giant solar-like oscillations.  By performing a literature search and comparing these targets’ per-pixel versus aperture light curves and PSDs, false positive or `blended’ targets were eliminated.  Starting in October 2021, time-series spectroscopic observations were taken of the remaining targets in order to look for signs of radial velocity motion.  Using the echelle spectrograph on the 3-meter telescope at Apache Point Observatory, 15 targets have been observed 3+ times.  Radial velocity measurements derived from these observations indicate the detection of at least 11 spectroscopic binaries, including one double-lined spectroscopic binary.

Once additional data are obtained to provide proper orbital phase coverage, the information derived from the scaling relations for red giant solar-like oscillations, spectral stellar atmosphere modeling, and dynamical binary star system modeling will allow for the computation of both stars’ stellar properties.  Ultimately, this information can then be used to perform stellar evolution and stellar pulsation modeling of the classical oscillations.  In this talk, I will provide a brief background on the importance of stellar pulsators in binary star systems, outline how the double-pulsator hidden binary targets were identified and false positives were eliminated, describe the methodology used to derive radial velocities from spectroscopic observations to determine the single or binary nature of the observed targets, and broadly outline the next steps and future goals of this project.

References:

Balona, L. A. 2018, MNRAS, 479, 183, doi: 10.1093/mnras/sty1511.

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A Visit to a Few High-Amplitude Delta Scuti Stars

Joyce A. Guzik¹, Richard Wagner², Karen Kinemuchi³, Ebraheem Farag^1,4, and Michael S. Soukup⁵

1) Los Alamos National Laboratory, Los Alamos, NM 87545 (joy@lanl.gov)

2) Leeside Observatory, Elgin, ON Canada

3) New Mexico State U., Las Cruces, NM 88003

4) Arizona State U., Tempe, AZ

5) Los Alamos National Laboratory (retired)

High-amplitude delta Scuti (HADS) stars are post-main-sequence stars with late-F through early A spectral type and masses 1.5 to 2.5 solar masses that pulsate in the fundamental and/or first overtone radial modes with amplitudes greater than 0.15 V-band magnitude (Watson et al. 2006). Like other delta Scuti stars, the periods of HADS are typically a few hours.

Space-based photometric data from, e.g., the NASA Kepler mission have shown that many HADS stars pulsate in additional non-radial modes, and that HADS are located throughout the instability strip at earlier evolutionary stages, so may not be distinct as a class from normal delta Scuti stars (Balona 2016). As is the case for other types of pulsating stars, there are many unresolved problems, such as the reasons for mode selection and amplitudes, and causes of amplitude and period changes (see, e.g., Guzik 2021).

HADS stars provide excellent targets for amateur observing because of their high amplitudes and short pulsation periods. Here we visit several delta Scuti stars which are targets of our ground-based observing program:  1) V1965 Aql, which shows a single period of 0.137 d; 2) LS Cet, the brightest and coolest of the four stars, with main period 0.0842 d; 3) RV Ari, a double-mode pulsator with amplitude ratio between fundamental and first overtone of 30%; 4) DDE 148, another double-mode pulsator that is also an eclipsing binary candidate.  Two of these stars also have light curves collected from the NASA TESS spacecraft.
 

We use Period04 (Lenz and Breger 2005) to derive pulsation frequencies and amplitudes from the light curves. Taking into account additional constraints from photometry and spectroscopy, we model the evolution and pulsations of these stars using the open-source MESA (Paxton et al. 2019) and GYRE (Townsend and Teitler 2013) codes and compare expectations from modeling with observations. We also apply the new RSP capability in MESA to model the hydrodynamics of radial pulsations of the envelopes of delta Scuti stars. 
 

References

Balona, L. A., Combination frequencies in high-amplitude δ Scuti stars, MNRAS 459, 1097 (2016).

Guzik, J. A., Highlights of Discoveries for δ Scuti Variable Stars from the Kepler Era, Frontiers in Astronomy and Space Sciences, Volume 8, id.55 (2021).

Lenz, P., and Breger, M., Communications in Asteroseismology 146, 53 (2005).

Paxton, B., et al., Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation, ApJS 243, 10 (2019).

Townsend, R. H. D. and Teitler, S. A., GYRE: an open-source stellar oscillation code based on a new Magnus Multiple Shooting scheme, MNRAS 435, 3406 (2013).

Watson, C. L., Henden, A. A., and Price, A., The International Variable Star Index (VSX), Soc. Astron. Sci. 25th Annu. Symp. Telesc. Sci., Vol. 25, Soc. Astron. Sci. (2006).

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