The classical Cepheid eta Aql was not included in past Leavitt Law work (Benedict et al. 2007) because of a presumed complicating orbit due to a known B9.8V companion. To determine the orbit of eta Aql B, we analyze a significant number of radial velocity measures (RV) from eight sources. With these we establish the RV variation due to Cepheid pulsation, using a twelve Fourier coefficient model, while solving for velocity offsets required to bring the RV data sets into coincidence. RV residuals provide no evidence of orbital motion, suggesting either nearly face-on orientation or very long period. Reanalysis of Hubble Space Telescope Fine Guidance Sensor astrometry now includes reference star parallax and proper motion priors from Gaia EDR3. As modeling confirmation, we reanalyze zeta Gem in parallel, deriving zeta Gem parallax and proper motion values consistent with Gaia EDR3, and consistent with the Benedict 2007 Leavitt Law. In an effort to further characterize eta Aql B, we hypothesize that eta Aql residuals larger than those of the associated reference stars or a parallax inconsistent with EDR3 and the Benedict 2007 Leavitt Law indicate unmodeled orbital motion. Using the astrometric noise or parallax mismatch with EDR3 we estimate possible periods and mass for eta Aql B. Ascribing photocenter motion to the photometric variation of the Cepheid, eta Aql A, yields a plausible separation, consistent with a long period, explaining the lack of RV variation. None of these approaches yields an unassailable characterization of the eta Aql A-B system

We believe that the extreme solar modulation of 3-60 MeV Galactic electrons measured by Voyager in the heliosheath and the interpretation of this new data in terms of the rigidity dependence of the diffusion coefficient at low rigidities presented in this paper represents a major step in understanding diffusion theory as it applies to energetic particles. This description uses electron spectra measured at 5 different epochs and distances within the heliosheath. The diffusion dependence needed to explain the remarkable solar modulation effects observed for both electrons and higher rigidity protons as one progresses from the heliopause inward by ~25 AU to the termination shock really has two distinct rigidity regimes. Above a rigidity ~Pc the diffusion coefficient has a dependence ~beta P, the modulation is ~P and its magnitude increases linearly with radius in AU according to the integral of dr/K. This integral defines a potential, beta, called the modulation potential, thus explaining the proton variations. At rigidities <Pc, the diffusion coefficient is ~beta and independent of rigidity. The modulation is also independent of rigidity but its magnitude depends on the modulation potential, thus explaining the electron modulation. One needs both electron and proton observations, together, to recognize the physical description of the solar modulation process. For the first time we have been able, using proton data at high rigidities and electron data at low rigidities, to put together a picture of the high and low rigidity diffusion coefficients and how they affect energetic particles in an astrophysical scale environment.

We have obtained phase-resolved optical spectroscopy of the old nova, and asynchronous polar V1500 Cyg. These new data reveal discrete cyclotron humps from two different strength magnetic fields. One region has B = 72 MG, while the other has B ~ 105 MG. With the detection of these features, we revisit the optical/near-IR light curves presented in Harrison & Campbell (2016), and find that the large photometric excesses observed in those data are fully reconcilable with cyclotron emission. These results, when combined with the X-ray observations that appeared to have maxima that repeated on the orbital period, imply that V1500 Cyg has reverted back to a synchronous polar. Using existing theory, we show that the strong field strengths found here can explain the rapid spin down time.

In this paper we compare galactic electron spectra measured up to TeV energies by AMS2 and CALET and that measured by Voyager at the lowest energies down to 1 MeV with that calculated using a Monte Carlo diffusion model for electron propagation in the galaxy. The observations and calculations at both ends of the electron spectrum, differing by a factor ~10^6 in energy, can be matched to within a few percent with a minimal set of assumptions. This includes an electron spectrum which has an index increasing from ~2.1 at the lowest energies to 2.4 at ~1 TeV, along with a diffusion coefficient that remains essentially constant below ~1.5 GV above which it becomes P^0.45. The Monte Carlo calculations indicate that the lowest and highest energy electrons originate within a local region near the galactic plane of size, less than L where L is the thickness of the trapping region. The remarkable agreement to within a few percent between the calculations and measurements from 20 GeV up to ~1 TeV also indicates that there are no individual sources greater than 10-20 percent of the Monte Carlo calculated background that are contributing to the observed electron intensity in this energy range.

We have used ATLAS12 to generate hydrogen-deficient stellar atmospheres to allow us to construct synthetic spectra to explore the possibility that the donor stars in some cataclysmic variables (CVs) are hydrogen deficient. We find that four systems, AE Aqr, DX And, EY Cyg, and QZ Ser have significant hydrogen deficits. We confirm that carbon and magnesium deficits, and sodium enhancements, are common among CV donor stars. The three Z Cam systems we observed are found to have solar metallicities and no abundance anomalies. Two of these objects, Z Cam and AH Her, have M-type donor stars; much cooler than expected given their long orbital periods. By using the combination of equivalent width measurements and light curve modeling, we have developed the ability to account for contamination of the donor star spectra by other luminosity sources in the binary. This enables more realistic assessments of secondary star metallicities. We find that the use of equivalent width measurements should allow for robust metallicities and abundance anomalies to be determined for CVs with M-type donor stars.

We report on a program to monitor classical novae (CNe) to determine if they produced dust in the ejecta created by their outbursts. Of the ten systems we followed, five produced dust. We also present limited infrared and optical spectroscopy of these objects. We present a complete $JHKLM$ spectrum for V992 Sco. V992 Sco was one of the brightest CNe in the infrared of all time, and our $M$-band spectrum of this object shows strong emission from the CO fundamental. We believe this to be the first, and only, spectroscopic observation of this feature in a CNe.

Using Hubble Space Telescope Fine Guidance Sensor astrometry and previously published radial velocity measures, we explore the exoplanetary system HD 202206. Our modeling results in a parallax, pi(abs) = 21.96 +/- 0.12 milliseconds of arc, a mass for HD 202206 B of M-B =0.089(-0.006)(+0.007) M-circle dot, and a mass for HD 202206 c of M-c = 17.9(-1.8)(+2.9) M-Jup. HD 202206 is a nearly face-on G + M binary orbited by a brown dwarf. The system architecture that we determine supports past assertions that stability requires a 5: 1 mean motion resonance (we find a period ratio, P-c/P-B= 4.92 +/- 0.04) and coplanarity (we find a mutual inclination, Phi = 6 degrees +/- 2 degrees).

Over the last 20 years, Hubble Space Telescope Fine Guidance Sensor interferometric astrometry has produced precise and accurate parallaxes of astrophysical interesting stars and mass estimates for stellar companions. We review parallax results, and binary star and exoplanet mass determinations, and compare a subset of these parallaxes with preliminary Gaia results. The approach to single-field relative astrometry described herein may continue to have value for targets fainter than the Gaia limit in the coming era of 20-30 m telescopes.

Hubble Space Telescope (HST) fine guidance sensor observations were used to obtain parallaxes of eight metal-poor ([Fe/H] < -1.4) stars. The parallaxes of these stars determined by the new Hipparcos reduction average 17% accuracy, in contrast to our new HST parallaxes, which average 1% accuracy and have errors on the individual parallaxes ranging from 85 to 144 mu as. These parallax data were combined with HST Advanced Camera for Surveys photometry in the F606W and F814W filters to obtain the absolute magnitudes of the stars with an accuracy of 0.02-0.03 mag. Six of these stars are on the main sequence (MS) (with -2.7 < [Fe/H] < -1.8) and are suitable for testing metal-poor stellar evolution models and determining the distances to metal-poor globular clusters (GCs). Using the abundances obtained by O'Malley et al., we find that standard stellar models using the VandenBerg & Clem color transformation do a reasonable job of matching five of the MS stars, with HD 54639 ([Fe/H] = -2.5) being anomalous in its location in the color-magnitude diagram. Stellar models and isochrones were generated using a Monte Carlo analysis to take into account uncertainties in the models. Isochrones that fit the parallax stars were used to determine the distances and ages of nine GCs (with -2.4 <= [Fe/H] <= -1.9). Averaging together the age of all nine clusters led to an absolute age of the oldest, most metal-poor GCs of 12.7 +/- 1.0 Gyr, where the quoted uncertainty takes into account the known uncertainties in the stellar models and isochrones, along with the uncertainty in the distance and reddening of the clusters.

We present new moderate-resolution near-infrared spectroscopy of three CVs obtained using GNIRS on GeminiNorth. These spectra covered three (CO)-C-13 bandheads found in the K-band, allowing us to derive the isotopic abundance ratios for carbon. We find small C-12/C-13 ratios for all three donor stars. In addition, these three objects show carbon deficits, with AE Aqr being the most extreme ([C/Fe] = -1.4). This result confirms the conjecture that the donor stars in some long-period CVs have undergone considerable nuclear evolution prior to becoming semi-contact binaries. In addition to the results for carbon, we find that the abundance of sodium is enhanced in these three objects, and the secondary stars in both RU Peg and SS Cyg suffer magnesium deficits. Explaining such anomalies appears to require higher mass progenitors than commonly assumed for the donor stars of CVs.

We have obtained a radial velocity curve for the L dwarf donor in WZ Sagittae using phase-resolved J-band spectra obtained with GNIRS on Gemini-north. We find a radial velocity semi-amplitude of K-2 525 11 km s(-1). This result reduces the error bar by a factor of three over previous attempts. A relatively strong, unidentified emission line centered near 1.177 mu m, corrupts the blue K I doublet in these data. While an H I emission feature near 1.2527 mu m distorts the depth of the red K I doublet. In addition, a weak H I emission line at 1.1969 mu m falls in the middle of the strongest FeH feature in these spectra. The combination of these contaminants prevents us from precisely constraining the spectral type of the donor. The strength of the absorption features remains consistent with an early L spectral type.

Analysis of a large set of phase-resolved K-band spectra of the cataclysmic variable WZ Sge shows that the secondary star of this system appears to be an L-dwarf. Previous K-band spectra of WZ Sge found that the CO overtone bandheads were in emission. We show that absorption from the (CO(2,0))-C-12 bandhead of the donor star creates a dip in the (CO(2,0))-C-12 emission feature. Measuring the motion of this feature over the orbital period, we construct a radial velocity curve that gives a velocity amplitude of K-abs = 520 +/- 35 km s(-1), consistent with the previously published values for this parameter.

We have used XMM–Newton and ground-based optical/near-infrared photometry to explore the old classical nova, and asynchronous polar V1500 Cyg. The X-ray light curve shows a single bright phase once per orbit, associated with the main accretion region. Analysis of the X-ray light curve indicates that the white dwarf spin period is now similar to the orbital period. When this inference is combined with the ground-based photometry, we find that the most probable explanation for the observed behaviour is a system that has become fully synchronized. The X-ray spectrum and luminosity of V1500 Cyg are consistent with a high state polar. The optical and near-IR light curves can partially be explained as a heavily irradiated secondary star, but exhibit strong deviations from that model. We find that the most likely explanation for the observed excesses in these light curves is cyclotron emission from distributed accretion regions, or from a multipole geometry.

We derive metallicities for 41 cataclysmic variables (CVs) from near-infrared spectroscopy. We use synthetic spectra that cover the 0.8 $\mu$m $\leq \lambda \leq$ 2.5 $\mu$m bandpass to ascertain the value of [Fe/H] for CVs with K-type donors, while also deriving abundances for other elements. Using calibrations for determining [Fe/H] from the $K$-band spectra of M-dwarfs, we derive more precise values for T$_{\rm eff}$ for the secondaries in the shortest period CVs, and examine whether they have carbon deficits. In general, the donor stars in CVs have sub-solar metallicities. We confirm carbon deficits for a large number of systems. CVs with orbital periods $>$ 5 hr are most likely to have unusual abundances. We identify four CVs with CO emission. We use phase-resolved spectra to ascertain the mass and radius of the donor in U Gem. The secondary star in U Gem appears to have a lower {\it apparent} gravity than a main sequence star of its spectral type. Applying this result to other CVs, we find that the later-than-expected spectral types observed for many CV donors is mostly an affect of inclination. All of the magnetic CVs, except the low accretion rate polar MQ Dra, have donors with subsolar metallicities. We find that two systems with unusual spectra, EI Psc and QZ Ser, that have large excesses of sodium, and extreme deficits of carbon. Synthetic spectra that have a reduced abundance of hydrogen are best able to explain the spectra of these two objects.

We have used XMM − Newton and ground-based optical/near-infrared photometry to explore the old classical nova, and asynchronous polar V1500 Cyg. The X-ray light curve shows a single bright phase once per orbit, associated with the main accretion region. Analysis of the X-ray light curve indicates that the white dwarf spin period is now similar to the orbital period. When this inference is combined with the ground-based photometry, we find that the most probable explanation for the observed behavior is a system that has become fully synchronized. The X-ray spectrum and luminosity of V1500 Cyg are consistent with a high state polar. The optical and near-IR light curves can partially be explained as a heavily irradiated secondary star, but exhibit strong deviations from that model. We find that the most likely explanation for the observed excesses in these light curves is cyclotron emission from distributed accretion regions, or from a multipole geometry.

We have used XMM-Newton and ground-based optical/near-infrared photometry to explore the old classical nova, and asynchronous polar V1500 Cyg. The X-ray light curve shows a single bright phase once per orbit, associated with the main accretion region. Analysis of the X-ray light curve indicates that the white dwarf spin period is now similar to the orbital period. When this inference is combined with the ground-based photometry, we find that the most probable explanation for the observed behaviour is a system that has become fully synchronized. The X-ray spectrum and luminosity of V1500 Cyg are consistent with a high state polar. The optical and near-IR light curves can partially be explained as a heavily irradiated secondary star, but exhibit strong deviations from that model. We find that the most likely explanation for the observed excesses in these light curves is cyclotron emission from distributed accretion regions, or from a multipole geometry.

We have extracted the WISE (Wide-field Infrared Survey Explorer) single-exposure data for a sample of 72 polars, which are highly magnetic cataclysmic variables (CVs). We combine these data with both published and unpublished optical and infrared data to explore the origins of the large amplitude variations seen in these systems. In nearly every case, we find evidence for cyclotron emission in the WISE bandpasses. We find that the derived magnetic field strengths for some polars are either too high, or cyclotron emission from lower field components, located spatially coincident to the main accreting poles, must be occurring. We have also estimated field strengths for a number of polars where no such values exist. In addition, contrary to expectations, we find that emission from the fundamental cyclotron harmonic (n = 1) appears to be nearly always present when the magnetic field is of the appropriate strength that it falls within a WISE bandpass. We find that the light curves for RBS 490, an ultrashort-period (46 minutes) CV, suggest that it is a polar. Modeling its spectrum indicates that its donor star is much hotter than expected. Nearly all of the detected polars show 11.5 mu m ("W3 band") excesses. The general lack of variability seen in the W3 bandpass light curves for higher-field polars demonstrates that these excesses are probably not due to cyclotron emission. There is circumstantial evidence that these excesses can be attributed to bremsstrahlung emission from their accretion streams. Reduction of the Spitzer 24 mu m image of V1500 Cyg shows that it appears to be located at the center of a small nebula.