We present the detection of an additional pulsation mode (7.35 mHz) of a subdwarf B star, PG 1613+426, and periodic Observed minus Calculated (O-C) variations for two existing pulsations. PG 1613+426 is near the hot end of the sdB... more
We present the detection of an additional pulsation mode (7.35 mHz) of a subdwarf B star, PG 1613+426, and periodic Observed minus Calculated (O-C) variations for two existing pulsations. PG 1613+426 is near the hot end of the sdB instability strip. One pulsation mode (6.94 mHz) was detected so far by Bonanno et al. (2002) and another pulsation mode candidate (7.05 mHz) was proposed with a confidence level above 90% by Kuassivi and Ferlet (2005). To constrain sdB star evolutional scenarios, this star was monitored in 2010, 2011, 2015, and 2017 as a part of a project for finding companions to sdB stars using the pulsation timing method. The photometric analysis of those data shows an additional 7.35 mHz pulsation mode as well as the previously detected 6.93 mHz mode. However the 7.05 mHz mode was not detected. Nightly amplitude changes of 7.35 mHz mode were observed in the 2011 data, however the 2017 data did not show nightly amplitude shifts. O-C variations were detected in both 6.9...
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Author(s): Hirshfeld, Alan; Bartlett, Jennifer Lynn; DeVorkin, David; Griffin, Elizabeth; Holbrook, Jarita; Oswalt, Terry; Rothenberg, Marc; Rumstay, Kenneth; Schechner, Sara; Tenn, Joseph; Trimble, Virginia | Abstract: This State of the... more
Author(s): Hirshfeld, Alan; Bartlett, Jennifer Lynn; DeVorkin, David; Griffin, Elizabeth; Holbrook, Jarita; Oswalt, Terry; Rothenberg, Marc; Rumstay, Kenneth; Schechner, Sara; Tenn, Joseph; Trimble, Virginia | Abstract: This State of the Profession White Paper from the American Astronomical Society’s Historical Astronomy Division (HAD) details HAD’s efforts to advance academic research in topics relating to the historical nature of astronomy, including the application of historical records to modern astrophysical problems, now and over the next decade.
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Aims. We aim to investigate variations in the arrival time of coherent stellar pulsations due to the light-travel time effect to test for the presence of sub-stellar companions. Those companions are the key to one possible formation... more
Aims. We aim to investigate variations in the arrival time of coherent stellar pulsations due to the light-travel time effect to test for the presence of sub-stellar companions. Those companions are the key to one possible formation scenario of apparently single sub-dwarf B stars. Methods. We made use of an extensive set of ground-based observations of the four large amplitude p-mode pulsators DW Lyn, V1636 Ori, QQ Vir, and V541 Hya. Observations of the TESS space telescope are available on two of the targets. The timing method compares the phase of sinusoidal fits to the full multi-epoch light curves with phases from the fit of a number of subsets of the original time series. Results. Observations of the TESS mission do not sample the pulsations well enough to be useful due to the (currently) fixed two-minute cadence. From the ground-based observations, we infer evolutionary parameters from the arrival times. The residual signals show many statistically significant periodic signals...
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We describe the remote facilities operated by the Southeastern Association for Research in Astronomy (SARA), a consortium of colleges and universities in the US partnered with Lowell Observatory, the Chilean National Telescope Allocation... more
We describe the remote facilities operated by the Southeastern Association for Research in Astronomy (SARA), a consortium of colleges and universities in the US partnered with Lowell Observatory, the Chilean National Telescope Allocation Committee, and the Instituto de Astrofisica de Canarias. SARA observatories comprise a 0.96m telescope at Kitt Peak, Arizona; a 0.6m instrument on Cerro Tololo, Chile; and the 1m Jacobus Kapteyn Telescope at the Roque de los Muchachos, La Palma, Spain. All are operated using standard VNC or Radmin protocols communicating with on-site PCs. Remote operation offers considerable flexibility in scheduling, allowing long-term observational cadences difficult to achieve with classical observing at remote facilities, as well as obvious travel savings. Multiple observers at different locations can share a telescope for training, educational use, or collaborative research programs. Each telescope has a CCD system for optical imaging, using thermoelectric cool...
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White dwarfs are the final remnants of low- and intermediate-mass stars. Their evolution is essentially a cooling process that lasts for ∼ 10 Gyr. Their observed properties provide information about the history of the Galaxy, its dark... more
White dwarfs are the final remnants of low- and intermediate-mass stars. Their evolution is essentially a cooling process that lasts for ∼ 10 Gyr. Their observed properties provide information about the history of the Galaxy, its dark matter content and a host of other interesting astrophysical problems. Examples of these include an independent determination of the past history of the local star formation rate, identification of the objects responsible for the reported microlensing events, constraints on the rate of change of the gravitational constant, and upper limits to the mass of weakly interacting massive particles. To carry on these tasks the essential observational tools are the luminosity and mass functions of white dwarfs, whereas the theoretical tools are the evolutionary sequences of white dwarf progenitors, and the corresponding white dwarf cooling sequences. In particular, the observed white dwarf luminosity function is the key manifestation of the white dwarf cooling ...
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Finding orbital solutions of binaries which have small mass ratios (<0.4) and long periods (>50 days) is challenging using traditional techniques. The radial velocity method is a good way to detect such binary stars, however it... more
Finding orbital solutions of binaries which have small mass ratios (<0.4) and long periods (>50 days) is challenging using traditional techniques. The radial velocity method is a good way to detect such binary stars, however it requires large telescopes. Therefore, the search for binaries in those regions is still incomplete. For binaries in this regime with at least one component that pulsates, pulsation timing is a better approach. Orbital solutions for such systems can be obtained from the periodic change in pulse arrival times as the star’s reflex motion is manifested by the changing distance along the line of sight. We present a search for binaries with ! Scuti variables in the Kepler K2 extended mission fields. We used the K2 long-cadence (sampling time = 29.45-min) light curves, which are suitable to detect pulsation periods of a few hours as in ! Scuti stars. The observation span for the Kepler K2 mission is about 80 days. Binary candidates which show evidence of perio...
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We argue that it is essential that the Astro2020 survey of the present state of American astronomy and the recommendations for the next decade address the issue of ensuring preservation of, and making more discoverable and accessible, the... more
We argue that it is essential that the Astro2020 survey of the present state of American astronomy and the recommendations for the next decade address the issue of ensuring preservation of, and making more discoverable and accessible, the field's rich legacy materials. These include both archived observations of scientific value and items of historical importance. Much of this heritage likely will be lost if action is not taken in the next decade. It is proposed that the decadal plan include recommendations on (1) compiling a list of historic sites and development of models for their preservation, (2) carrying out a comprehensive inventory of astronomy's archival material, and (3) digitizing, with web-based publication, those photographs and papers judged to have the most value for scientific and historical investigations. The estimated cost for an example project on plate preservation is a one-time investment of less than $10 million over ten years plus the typical on-going...
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PG 1219 + 534 (KY Uma) is a subdwarf B pulsating star with multiple periodicities between 120 – 175 s. PG 1219 + 534 was monitored for 90 hours during 2010-1 and 2016 using the 0.9m SARA-KP telescope at Kitt Peak National Observatory... more
PG 1219 + 534 (KY Uma) is a subdwarf B pulsating star with multiple periodicities between 120 – 175 s. PG 1219 + 534 was monitored for 90 hours during 2010-1 and 2016 using the 0.9m SARA-KP telescope at Kitt Peak National Observatory (KPNO) in Arizona and the 0.8 m Ortega telescope at Florida Institute of Technology in Melbourne, Florida. So far, the most promising theory for the origin of subdwarf B (sdB) stars is that they result from binary mass transfer near the Helium Flash stage of evolution. The observations of PG 1219+534 reported here are part of our program to constrain this evolutional theory by searching for companions and determining orbital separations around sdB pulsators using the Observed-minus-Calculated (O-C) method. A star’s position in space will wobble due to the gravitational forces of any companion or planet. If the star emits periodic signal like pulsations, its orbital motion around the system’s center of mass causes periodic changes in the light pulse arri...
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Previous studies on the subject of eclipsing binaries (EBs) within the Kepler field have been adequately determined the period, distance, and other stellar parameters of these systems (Borkovits, et al. 2015). Additionally, with the use... more
Previous studies on the subject of eclipsing binaries (EBs) within the Kepler field have been adequately determined the period, distance, and other stellar parameters of these systems (Borkovits, et al. 2015). Additionally, with the use of Observed-minus-Calculated (O-C) plots, variation in the timing of timing of eclipses can be easily detected. The eclipse timing shifts may be caused by dynamical effects or by light-travel time effects (LTTE) caused by the existence of a third body. The following research was conducted on ten binaries within the Kepler “K2” Campaign 5 field whose light curves (LCs) showed evidence of eclipses with periods shorter than ten days. The timings of the eclipses were then investigated using the O-C method to search for variations and, if so, to deduce the cause of such variations and to determine the parameters of the binary. Acknowledgments References Otani, T. PhD Thesis, 2015, Florida Institute of Technology. Borkovits, T., et al. “A Comprehensive Stu...
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We are determining rotation periods for an ensemble of over 100 wide non-interacting binary stars in the K2 Campaign 5 field that contain two main sequence dwarfs, as well as a smaller sample containing at least one white dwarf component.... more
We are determining rotation periods for an ensemble of over 100 wide non-interacting binary stars in the K2 Campaign 5 field that contain two main sequence dwarfs, as well as a smaller sample containing at least one white dwarf component. Observations of such coeval pairs provide the basis for our new investigation of rotation-based age determinations. Such “gyrochronology” ages can achieve a precision that exceeds most other current method of stellar age determination. Here we present a status report on our analysis of the light curves extracted from the K2 Campaign 5 field. Fig. 7 – Rotation period vs. B-V (a proxy for mass) for 12 binaries in the C5 field. From bottom, dashed blue lines are constant gyrochrones for 0.25, 0.50 and 1 to 10 Gyr (in 1 Gyr increments) from Angus et al. (2015, MNRAS 450, 1787). Large dots are stars with B-V data; small dots indicate B-V values estimated from ugriz data. Solid/dashed lines connect components with/without consistent rotation ages, respec...
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Author(s): Lattis, James; Osborn, Wayne; Bartlett, Jennifer Lynn; Griffin, Elizabeth; Hockey, Thomas; McCluskey, Stephen; Oswalt, Terry; Pevtsov, Alexei A; Schechner, Sara; Trimble, Virginia | Abstract: We argue that it is essential that... more
Author(s): Lattis, James; Osborn, Wayne; Bartlett, Jennifer Lynn; Griffin, Elizabeth; Hockey, Thomas; McCluskey, Stephen; Oswalt, Terry; Pevtsov, Alexei A; Schechner, Sara; Trimble, Virginia | Abstract: We argue that it is essential that the Astro2020 survey of the present state of American astronomy and the recommendations for the next decade address the issue of ensuring preservation of, and making more discoverable and accessible, the field’s rich legacy materials. These include both archived observations of scientific value and items of historical importance. Much of this heritage likely will be lost if action is not taken in the next decade. It is proposed that the decadal plan include recommendations on (1) compiling a list of historic sites and development of models for their preservation, (2) carrying out a comprehensive inventory of astronomy’s archival material, and (3) digitizing, with web-based publication, those photographs and papers judged to have the most value for s...
Open-access telescopes of all apertures are needed to operate a competitive and efficient national science program. While larger facilities contribute light-gathering power and angular resolution, smaller ones dominate for field of view,... more
Open-access telescopes of all apertures are needed to operate a competitive and efficient national science program. While larger facilities contribute light-gathering power and angular resolution, smaller ones dominate for field of view, time-resolution, and especially, total available observing time, thereby enabling our entire, diversely-expert community. Smaller aperture telescopes therefore play a critical and indispensable role in advancing science. Thus, the divestment of NSF support for modest-aperture (1 - 4 m) public telescopes poses a serious threat to U.S. scientific leadership, which is compounded by the unknown consequences of the shift from observations driven by individual investigators to survey-driven science. Given the much higher cost efficiency and dramatic science returns for investments in modest aperture telescopes, it is hard to justify funding only the most expensive facilities. We therefore urge the Astro2020 panel to explicitly make the case for modest ape...
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The Gaia DR2 has dramatically increased the ability to detect faint nearby white dwarfs. The census of the local white dwarf population has recently been extended from 25 pc to 50 pc, effectively increasing the sample by roughly an order... more
The Gaia DR2 has dramatically increased the ability to detect faint nearby white dwarfs. The census of the local white dwarf population has recently been extended from 25 pc to 50 pc, effectively increasing the sample by roughly an order of magnitude. Here we examine the completeness of this new sample as a function of variables such as apparent magnitude, distance, proper motion, photometric color index, unresolved components, etc.
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The accuracy with which infrared photometry can be carried out is currently limited by poor definition of the instrumental system and by the accuracy of the available standard stars. We present new colour transformations between the CIT... more
The accuracy with which infrared photometry can be carried out is currently limited by poor definition of the instrumental system and by the accuracy of the available standard stars. We present new colour transformations between the CIT J, H, K photometric system and systems currently in use at Cerro Tololo, Mauna Kea and Kitt Peak. The precision of the J, H, K data for some of the stars observed by Elias et al. is improved and the system extended to fainter stars suitable for use with larger telescopes and/or infrared arrays. Evidence of infrared variability has been detected for one M dwarf star in our programme.
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Using B, V, R, I photometric parallaxes for components of wide binaries, new bolometric corrections by Bergeron et al. (1995) and cooling curves by Wood (1995), we have determined the white dwarf luminosity function (WDLF; Oswalt et al.... more
Using B, V, R, I photometric parallaxes for components of wide binaries, new bolometric corrections by Bergeron et al. (1995) and cooling curves by Wood (1995), we have determined the white dwarf luminosity function (WDLF; Oswalt et al. 1996). A minimum age of 9.5+1.1−0.8 Gyr is implied for the Galactic disk; arbitrarily old models are consistent at the +2σ level. Smith (1997) confirms these results using a much larger sample and similar methodology. Using these same new models, Wood & Oswalt (1997) show that the WDLF of Liebert et al. (1988) yields an age of 7.5+0.5−0.5 Gyr, more than 20% younger than their original estimate.
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Abstract The spectroscopic properties of faint binaries selected from the Luyter and Gicias, et al., proper motion surveys were analyzed. Roughly one dozen white dwarfs were identified. Based on a comparison of the UBV magnitudes and... more
Abstract The spectroscopic properties of faint binaries selected from the Luyter and Gicias, et al., proper motion surveys were analyzed. Roughly one dozen white dwarfs were identified. Based on a comparison of the UBV magnitudes and colors exhibited by the component ...
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ABSTRACT We report preliminary results of a search for variability among cool white dwarf stars. Targets were selected on the basis of photometric BVRI colors, large reduced proper motion and spectroscopic absorption features such as H,... more
ABSTRACT We report preliminary results of a search for variability among cool white dwarf stars. Targets were selected on the basis of photometric BVRI colors, large reduced proper motion and spectroscopic absorption features such as H, H2, or C2. Unfiltered time series CCD images were obtained with the SARA Observatory 0.9-m telescope at Kitt Peak for 11 stars and analyzed using a Discrete Fourier Transform (DFT) procedure. The program objects ranged in color from 0 &lt; R-I &lt; 1.0, and in reduced proper motion from 17 &lt; HR &lt; 22. Several may be members of the Galactic halo. All are near the low luminosity end of the white dwarf cooling track. Within the range of color and luminosity searched so far, no periodic variations larger than ~0.04 magnitude have been detected. We gratefully acknowledge the Southeastern Association for Research in Astronomy (SARA) Research Experiences for Undergraduates internship program which is supported by the National Science Foundation through a grant to Florida Tech (AST-0097616).
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Accurate distances and luminosities for white dwarfs help establish a number of basic observational properties for degenerate stars. Such collective properties as luminosity functions, space densities, and space motions are all tied... more
Accurate distances and luminosities for white dwarfs help establish a number of basic observational properties for degenerate stars. Such collective properties as luminosity functions, space densities, and space motions are all tied directly to reliable distance estimates for large numbers of stars. As the number of direct trigonometric parallaxes will remain limited for the near future, we apply the recent results of improved photometric calibrations to large samples of white dwarfs having high quality optical and near IR photometry, as well as spectroscopic temperatures and gravities. Improved photometric distances (and luminosities) are estimated. Comparisons with trigonometric parallaxes and the determination of residual reddening will be discussed, as well as estimates of distance uncertainty. This work is supported by NSF Grants AST 0507797 (JH) and AST 0206115 (TO).
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ABSTRACT Currently the most complete sample of white dwarf stars comes from the local white dwarf population within 20 pc, which is believed to be 80 percent complete. This sample contains some 132 degenerate stars. We hope to effectively... more
ABSTRACT Currently the most complete sample of white dwarf stars comes from the local white dwarf population within 20 pc, which is believed to be 80 percent complete. This sample contains some 132 degenerate stars. We hope to effectively double the number of known local white dwarfs by extending the sample boundary to 25 pc, while still maintaining a high level of completeness. We discuss plans for extending the local sample and some of the studies that will be possible with this enlarged population. This work was funded in part by NSF Grant AST-1008845.
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ABSTRACT We propose to complete our study of M dwarf/white dwarf binary systems with the goal of determining the correlation between the chromospheric activity and ages of M dwarf stars for ages up to the age of the galactic disk (~M7-8;... more
ABSTRACT We propose to complete our study of M dwarf/white dwarf binary systems with the goal of determining the correlation between the chromospheric activity and ages of M dwarf stars for ages up to the age of the galactic disk (~M7-8; ~10 Gyr). This project is unique in that it uses the well determined age of the white dwarf to establish the age of the M dwarf in the binary system. Previous studies used open clusters for age determination, and were confined to ages &lt; 5 Gyr. These indicated the surprising result that the age at which activity ceased depended on the mass (temperature, color) of the M dwarf, in contrast to the well known Skumanich relation for early type F-G-K stars where the age-activity relation is a manifestation of the rotational velocity evolution. Such a different age-activity relation has important consequences for understanding the dynamo generation of the magnetic fields in the lowest mass stars and brown dwarfs, and the different manifestations of the magnetic activity compared to solar-type stars.
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The closures of 1-4m telescopes at several international facilities over the past decade have been cause for lament in the astronomical community. However the future of small telescopes in the dawning era of giants should be quite bright... more
The closures of 1-4m telescopes at several international facilities over the past decade have been cause for lament in the astronomical community. However the future of small telescopes in the dawning era of giants should be quite bright if creative steps are taken. This paper will address some of the scientific and productivity issues that argue persuasively that a strong partnership between small efficient telescopes and the new generation of giant telescopes is essential. For example among a host of functions that can best be performed by small telescopes are the development of innovative approaches to operations instrumentation and unique research projects. To accomplish these it will be essential to improve the operational efficiency of existing small facilities via more frequent use of standard off-the-shelf technology optimization of individual telescopes for special projects increased use of active and adaptive optics automation and remote access. A selection of scientific initiatives will be presented that are ideally suited for new (or renovated) small telescopes.