The eclipsing binary system 2M 1938+4603 consists of a pulsating hot subdwarf B star and a cool M dwarf companion in an effectively circular three-hour orbit. The light curve shows both primary and ...secondary eclipses, along with a strong reflection effect from the cool companion. Here, we present constraints on the component masses and eccentricity derived from the Romer delay of the secondary eclipse. Using six months of publicly available Kepler photometry obtained in short-cadence mode, we fit model profiles to the primary and secondary eclipses to measure their centroid values. We find that the secondary eclipse arrives on average 2.06 + or - 0.12 s after the midpoint between primary eclipses. Under the assumption of a circular orbit, we calculate from this time delay a mass ratio of q = 0.2691 + or - 0.0018 and individual masses of M sub(sd) = 0.372 + or - 0.024 M sub(middot in circle) and M sub(c) = 0.1002 + or - 0.0065 M sub(middot in circle) for the sdB and M dwarf, respectively. These results differ slightly from those of a previously published light-curve modeling solution; this difference, however, may be reconciled with a very small eccentricity, e cos omega asymptotically = 0.00004. We also report a decrease in the orbital period of P = (-1.23 + or - 0.07) x 10 super(-10).
Hot subdwarf stars with F-K main sequence binary companions have been known for decades, but the first orbital periods for such systems were published just recently. Current observations suggest that ...most have long periods, on the order of years, and that some are or once were hierarchical triple systems. As part of a survey with the Hobby-Eberly Telescope, we have been monitoring the radial velocities of several composite-spectra binaries since 2005 in order to determine their periods, velocities, and eccentticities. Here we present observations and orbital solutions for two of these systems, PG 1449+653 and PG 1701+359. Similar to the other sdB+F/G/K binaries with solved orbits, their periods are long, 909 and 734 days, respectively, and pose a challenge to current binary population synthesis models of hot subdwarf stars. Intrigued by their relatively large systemic velocities, we also present a kinematical analysis of both targets and find that neither is likely a member of the Galactic thin disk.
Many hot subdwarf stars show composite spectral energy distributions indicative of cool main-sequence (MS) companions. Binary population synthesis (BPS) models demonstrate such systems can be formed ...via Roche lobe overflow or common envelope evolution but disagree on whether the resulting orbital periods will be long (years) or short (days). Few studies have been carried out to assess the orbital parameters of these spectroscopic composite binaries; current observations suggest the periods are long. To help address this problem, we selected 15 moderately bright (V ~ 13) hot subdwarfs with F-K dwarf companions and monitored their radial velocities from 2005 January to 2008 July using the bench-mounted Medium Resolution Spectrograph on the Hobby-Eberly Telescope (HET). Here we describe the details of our observing, reduction, and analysis techniques, and present preliminary results for all targets. By combining the HET data with recent observations from the Mercator Telescope, we are able to calculate precise orbital solutions for three systems using more than six years of observations. We also present an up-to-date period histogram for all known hot subdwarf binaries, which suggests those with F-K MS companions tend to have orbital periods on the order of several years. Such long periods challenge the predictions of conventional BPS models, although a larger sample is needed for a thorough assessment of the models' predictive success. Lastly, one of our targets has an eccentric orbit, implying some composite-spectrum systems might have formerly been hierarchical triple systems, in which the inner binary merged to create the hot subdwarf.
This paper presents the first results from draw-a-scientist tests (DASTs) over five years that were used to measure the effect of 8-10 week long astronomy clubs and week long summer camps on 3rd-5th ...grade elementary school students' perceptions of scientists. We facilitated these DASTs prior to these clubs or camps, which provide a baseline for a student's initial conception of scientists, and once at the end, to determine whether their conception changed, possibly as a result of their involvement. In total we analyze 89 pairs of DASTs using a numerical grading scheme designed to quantify the presence of various features in the drawn scientist and their activities. We find that there is a gender imbalance in both the pre- and postclub drawings, with only 32% and 35%, respectively, of students drawing female scientists. We also find that a third to a half of the scientists have a stereotypical appearance and/or are performing stereotypical activities. Although we find insignificant changes (<5%) in most categories, we do find an 8% increase in the number of scientists that have a stereotypical appearance, which is worth following up, but a significant 12% decrease in the number of scientists who are performing stereotypical activities. In addition, we present some possible improvements to implementing DASTs and discuss other possible assessments that could provide a more direct method of gauging the effect of these astronomy clubs or camps.
The demographics of dwarf galaxy populations have long been in tension with predictions from the Cold Dark Matter (CDM) paradigm. If primordial density fluctuations were scale-free as predicted, ...dwarf galaxies should themselves host dark matter subhaloes, the most massive of which may have undergone star formation resulting in dwarf galaxy groups. Ensembles of dwarf galaxies are observed as satellites of more massive galaxies, and there is observational and theoretical evidence to suggest that these satellites at z=0 were captured by the massive host halo as a group. However, the evolution of dwarf galaxies is highly susceptible to environment making these satellite groups imperfect probes of CDM in the low mass regime. We have identified one of the clearest examples to date of hierarchical structure formation at low masses: seven isolated, spectroscopically confirmed groups with only dwarf galaxies as members. Each group hosts 3-5 known members, has a baryonic mass of ~4.4 x 10^9 to 2 x 10^10 Msun, and requires a mass-to-light ratio of <100 to be gravitationally bound. Such groups are predicted to be rare theoretically and found to be rare observationally at the current epoch and thus provide a unique window into the possible formation mechanism of more massive, isolated galaxies.
The eclipsing binary system 2M 1938+4603 consists of a pulsating hot subdwarf
B star and a cool M dwarf companion in an effectively circular three-hour
orbit. The light curve shows both primary and ...secondary eclipses, along with a
strong reflection effect from the cool companion. Here we present constraints
on the component masses and eccentricity derived from the R{\o}mer delay of the
secondary eclipse. Using six months of publicly-available Kepler photometry
obtained in Short Cadence mode, we fit model profiles to the primary and
secondary eclipses to measure their centroid values. We find that the secondary
eclipse arrives on average 2.06 +/- 0.12 s after the midpoint between primary
eclipses. Under the assumption of a circular orbit, we calculate from this time
delay a mass ratio of q = 0.2691 +/- 0.0018 and individual masses of M_sd =
0.372 +/- 0.024 Msun and M_c = 0.1002 +/- 0.0065 Msun for the sdB and M dwarf,
respectively. These results differ slightly from those of a
previously-published light curve modeling solution; this difference, however,
may be reconciled with a very small eccentricity, e cos \omega\ ~ 0.00004. We
also report an orbital period decrease of P-dot = (-1.23 +/- 0.07) x 10^-10.
Hot subdwarf stars with F-K main sequence binary companions have been known for decades, but the first orbital periods for such systems were published just recently. Current observations suggest that ...most have long periods, on the order of years, and that some are or once were hierarchical triple systems. As part of a survey with the Hobby-Eberly Telescope, we have been monitoring the radial velocities of several composite-spectra binaries since 2005 in order to determine their periods, velocities, and eccentricities. Here we present observations and orbital solutions for two of these systems, PG 1449+653 and PG 1701+359. Similar to the other sdB+F/G/K binaries with solved orbits, their periods are long, 909 d and 734 d, respectively, and pose a challenge to current binary population synthesis models of hot subdwarf stars. Intrigued by their relatively large systemic velocities, we also present a kinematical analysis of both targets and find that neither is likely a member of the Galactic thin disk.
Many hot subdwarf stars show composite spectral energy distributions indicative of cool main sequence companions. Binary population synthesis (BPS) models demonstrate such systems can be formed via ...Roche lobe overflow or common envelope evolution but disagree on whether the resulting orbital periods will be long (years) or short (days). Few studies have been carried out to assess the orbital parameters of these spectroscopic composite binaries; current observations suggest the periods are long. To help address this problem, we selected fifteen moderately-bright (V~13) hot subdwarfs with F-K dwarf companions and monitored their radial velocities (RVs) from January 2005 to July 2008 using the bench-mounted Medium Resolution Spectrograph on the Hobby-Eberly Telescope (HET). Here we describe the details of our observing, reduction, and analysis techniques and present preliminary results for all targets. By combining the HET data with recent observations from the Mercator telescope, we are able to calculate precise orbital solutions for three systems using more than 6 years of observations. We also present an up-to-date period histogram for all known hot subdwarf binaries, which suggests those with F-K main sequence companions tend to have orbital periods on the order of several years. Such long periods challenge the predictions of conventional BPS models, although a larger sample is needed for a thorough assessment of the models' predictive success. Lastly, one of our targets has an eccentric orbit, implying some composite-spectrum systems might have formerly been hierarchical triple systems, in which the inner binary merged to create the hot subdwarf.
The eclipsing binary system 2M 1938+4603 consists of a pulsating hot subdwarf B star and a cool M dwarf companion in an effectively circular three-hour orbit. The light curve shows both primary and ...secondary eclipses, along with a strong reflection effect from the cool companion. Here we present constraints on the component masses and eccentricity derived from the Rømer delay of the secondary eclipse. Using six months of publicly-available Kepler photometry obtained in Short Cadence mode, we fit model profiles to the primary and secondary eclipses to measure their centroid values. We find that the secondary eclipse arrives on average 2.06 +/- 0.12 s after the midpoint between primary eclipses. Under the assumption of a circular orbit, we calculate from this time delay a mass ratio of q = 0.2691 +/- 0.0018 and individual masses of M_sd = 0.372 +/- 0.024 Msun and M_c = 0.1002 +/- 0.0065 Msun for the sdB and M dwarf, respectively. These results differ slightly from those of a previously-published light curve modeling solution; this difference, however, may be reconciled with a very small eccentricity, e cos \omega\ ~ 0.00004. We also report an orbital period decrease of P-dot = (-1.23 +/- 0.07) x 10^-10.
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