Accurate pre- and post-eruption orbital periods for the dwarf/classical nova V1017 Sgr

V1017 Sgr is a classical nova (from 1919) that displayed an earlier dwarf nova eruption (from 1901) and underwent two more dwarf nova events (in 1973 and 1991). Previous work on this bright system in quiescence (V = 13.5) has consisted only of a few isolated magnitudes, a few spectra and an ambiguous claim of an orbital period of 5.714 d based on nine radial velocities. To test this period, we have collected 2896 magnitudes (plus 53 in the literature) in the UBVRIJHKL bands from 1897-2016, making an essentially complete photometric history of this unique cataclysmic variable. We find that the light curve in all bands is dominated by the ellipsoidal modulations of a G giant companion star, with a post-eruption (after the 1919 nova event) orbital period of 5.786290 ± 0.000032 d. This is the longest period for any classical nova; the accretion must be powered by the nuclear evolution of the companion star and dwarf nova events occur only because the outer parts of the large disc are cool enough to be unstable. Further, we measure the pre-eruption orbital period (from 1907-1916). The orbital period has decreased by 273 ± 61 parts per million across the 1919 eruption, with the significance of the period change being at the 5.7σ confidence level. This is startling and mystifying for nova theory, because the three known period-change effects cannot account for a period decrease in V1017 Sgr, much less one of such a large size

The Centrality of the Center: Best Practices for Engaging Students on Campus

Communication centers exist primarily as a complementary student service (Strawser, Apostel, Carpenter, Cuny, Dvorak, & Head, 2019). As an integral campus student services, centers must place an overarching emphasis on student engagement. Student engagement, according to NSSE, is the time and effort students put into their educational activities and the institutional deployment of educational resources. Communication centers, to continue to prove their value to institutions, must continue to build programming and initiatives that are worthy of students’ time and get students to participate. To address engagement concerns, the authors of this essay offer ten best practices for building and sustaining student engagement in the communication center. The best practices are universal and transferable, meaning, any center, no matter the vision or the resources, could theoretically implement the ideas

The orbital and superhump periods of the dwarf nova SDSS J093249.57+472523.0

We report unfiltered CCD photometry of the eclipsing dwarf nova SDSS J093249.57+472523.0 obtained during its first confirmed outburst in 2011 March. The outburst amplitude was at least 3.0 magnitudes above mean quiescence and it lasted at least 11 days, although we missed the beginning of the outburst. Superhumps having peak-to-peak amplitude up to 0.3 magnitudes were present during the outburst, thereby establishing it to be a member of the SU UMa family. The mean superhump period was Psh = 0.06814(11) d. Analysis of our measurements of eclipse times of minimum, supplemented with data from other researchers, allowed us to measure the orbital period as Porb = 0.06630354(5) d. The superhump period excess was epsilon = 0.028(1) which is consistent with of SU UMa systems of similar Porb. The FWHM eclipse duration varied between 6 and 13 mins and the eclipse depth was up to 1.6 magnitudes.Comment: 15 pages, 4 figures. Accepted for publication in Journal of the British Astronomical Associatio