Abstract
Using an extensive archive for visual observations from the AAVSO, along with published times of maximum light, we determined a new model for the period of X Cygni. The best model is two ...linear fits for data before and after 1917 (JD2421512). Before that time the period is 16.38438 ± 0.00036 days. After we find a period of 16.386470 ± 0.000028 days. An examination of the O-C values for data after 1917 shows no clear evidence of a constant period change or of sinusoidal variations. The period looks to be constant. From an examination of H-alpha index measurements we find a drop in the value between data before 2013 October and data after 2014 July. This drop is not related to temperature and is likely related to mass loss in the star. Finally, we find that radial-velocity measurements match well with previously published values and show no seasonal variation over the 11 yr of data. This again seems to limit the possibility of a companion.
Abstract
A variety of interesting objects such as Wolf–Rayet stars, tight OB associations, planetary nebulae, X-ray binaries, etc., can be discovered as point or compact sources in H
α
surveys. How ...these objects distribute through a galaxy sheds light on the galaxy star formation rate and history, mass distribution, and dynamics. The nearby galaxy M33 is an excellent place to study the distribution of H
α
-bright point sources in a flocculant spiral galaxy. We have reprocessed an archived WIYN continuum-subtracted H
α
image of the inner 6.′5 × 6.′5 of M33 and, employing both eye and machine searches, have tabulated sources with a flux greater than approximately 10
−15
erg cm
−2
s
−1
. We have effectively recovered previously mapped H
ii
regions and have identified 152 unresolved point sources and 122 marginally resolved compact sources, of which 39 have not been previously identified in any archive. An additional 99 H
α
sources were found to have sufficient archival flux values to generate a Spectral Energy Distribution. Using the SED, flux values, H
α
flux value, and compactness, we classified 67 of these sources.
The Seyfert 1 galaxy Zw 229-015 is among the brightest active galaxies being monitored by the Kepler mission. In order to determine the black hole mass in Zw 229-015 from H Delta *b reverberation ...mapping, we have carried out nightly observations with the Kast Spectrograph at the Lick 3 m telescope during the dark runs from 2010 June through December, obtaining 54 spectroscopic observations in total. We have also obtained nightly V-band imaging with the Katzman Automatic Imaging Telescope at Lick Observatory and with the 0.9 m telescope at the Brigham Young University West Mountain Observatory over the same period. We detect strong variability in the source, which exhibited more than a factor of two change in broad H Delta *b flux. From cross-correlation measurements, we find that the H Delta *b light curve has a rest-frame lag of 3.86+0.69 --0.90 days with respect to the V-band continuum variations. We also measure reverberation lags for H Delta *a and H Delta *g and find an upper limit to the H Delta *d lag. Combining the H Delta *b lag measurement with a broad H Delta *b width of Delta *sline = 1590 ? 47 km s--1 measured from the rms variability spectrum, we obtain a virial estimate of M BH = 1.00+0.19 --0.24 X 107 M for the black hole in Zw 229-015. As a Kepler target, Zw 229-015 will eventually have one of the highest-quality optical light curves ever measured for any active galaxy, and the black hole mass determined from reverberation mapping will serve as a benchmark for testing relationships between black hole mass and continuum variability characteristics in active galactic nuclei.
We used point-spread function fitting and a differential ensemble determined from a robust median statistic (RoMS) to examine stars in six open clusters in a search for d Scuti variables. In the ...search for new variable stars among hundreds or thousands of stars, the RoMS is proved more effective for finding low-amplitude variables than the traditional error-curve approach. This high-precision differential approach was applied to the open clusters NGC 225, NGC 559, NGC 6811, NGC 6940, NGC 7142, and NGC 7160. Thirteen variables, 29 suspected variables, and 65 potential variables were found, and time-series data of the variables are presented. Among the 13 variables we found nine new d Scuti variables.
We define an Hα photometric system that is designed as a companion to the well established Hβ index. The new system is built on spectrophotometric observations of field stars as well as stars in ...benchmark open clusters. We present data for 75 field stars, 12 stars from the Coma star cluster, 24 stars from the Hyades, 17 stars from the Pleiades, and 8 stars from NGC 752 to be used as primary standard stars in the new systems. We show that the system transformations are relatively insensitive to the shape of the filter functions. We make comparisons of the Hα index to the Hβ index and illustrate the relationship between the two systems. In addition, we present relations that relate both hydrogen indices to equivalent width and effective temperature. We derive equations to calibrate both systems for Main Sequence stars with spectral types in the range O9 to K2 for equivalent width and A2 to K2 for effective temperature.
We report the first discovery of a transiting circumbinary planet detected from a single sector of Transiting Exoplanet Survey Satellite (TESS) data. During Sector 21, the planet TIC 172900988b ...transited the primary star and then five days later it transited the secondary star. The binary is itself eclipsing, with a period P ≈ 19.7 days and an eccentricity e ≈ 0.45. Archival data from ASAS-SN, Evryscope, KELT, and SuperWASP reveal a prominent apsidal motion of the binary orbit, caused by the dynamical interactions between the binary and the planet. A comprehensive photodynamical analysis of the TESS, archival and follow-up data yields stellar masses and radii of M(1) = 1.2384 ± 0.0007 Mꙩ and R(1) = 1.3827 ± 0.0016 Rꙩ for the primary and M(2) = 1.2019 ± 0.0007 Mꙩ and R(2) = 1.3124 ± 0.0012 Rꙩ for the secondary. The radius of the planet is R(3) = 11.25 ± 0.44 Rꚛ (1.004 ± 0.039R(Jup)). The planet’s mass and orbital properties are not uniquely determined—there are six solutions with nearly equal likelihood. Specifically, we find that the planet’s mass is in the range of 824 ≲ M3 ≲ 981 Mꚛ (2.65 ≲ M3 ≲ 3.09M(Jup)), its orbital period could be 188.8, 190.4, 194.0, 199.0, 200.4, or 204.1 days, and the eccentricity is between 0.02 and 0.09. At V = 10.141 mag, the system is accessible for high-resolution spectroscopic observations, e.g., the Rossiter–McLaughlin effect and transit spectroscopy.
A variety of interesting objects such as Wolf-Rayet stars, tight OB associations, planetary nebulae, X-ray binaries, etc., can be discovered as point or compact sources in H surveys. How these ...objects distribute through a galaxy sheds light on the galaxy star formation rate and history, mass distribution, and dynamics. The nearby galaxy M33 is an excellent place to study the distribution of H -bright point sources in a flocculant spiral galaxy. We have reprocessed an archived WIYN continuum-subtracted H image of the inner 6 5 × 6 5 of M33 and, employing both eye and machine searches, have tabulated sources with a flux greater than approximately 10−15 erg cm−2s−1. We have effectively recovered previously mapped H ii regions and have identified 152 unresolved point sources and 122 marginally resolved compact sources, of which 39 have not been previously identified in any archive. An additional 99 H sources were found to have sufficient archival flux values to generate a Spectral Energy Distribution. Using the SED, flux values, H flux value, and compactness, we classified 67 of these sources.
ABSTRACT We define an H photometric system that is designed as a companion to the well established Hβ index. The new system is built on spectrophotometric observations of field stars as well as stars ...in benchmark open clusters. We present data for 75 field stars, 12 stars from the Coma star cluster, 24 stars from the Hyades, 17 stars from the Pleiades, and 8 stars from NGC 752 to be used as primary standard stars in the new systems. We show that the system transformations are relatively insensitive to the shape of the filter functions. We make comparisons of the H index to the Hβ index and illustrate the relationship between the two systems. In addition, we present relations that relate both hydrogen indices to equivalent width and effective temperature. We derive equations to calibrate both systems for Main Sequence stars with spectral types in the range O9 to K2 for equivalent width and A2 to K2 for effective temperature.
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