Unusual rainbows as auroral candidates: another point of view [SSA]


Several auroral events that occurred in the past have not been catalogued as such due to fact that they were described in the historical sources with different terminology. Hayakawa et al. (2016) have reviewed historical oriental chronicles and have proposed the terms “unusual rainbow” and “white rainbow” as candidates to auroras. In this work, we present three events that took place in the 18th century in two different settings (the Iberian Peninsula and Brazil) that were originally described with similar definition/wording used by the oriental chronicles, despite the inherent differences in terms associated to oriental and Latin languages. We show that these terms are indeed applicable to the three case studies from Europe and South America. Thus, the auroral catalogues available can be extended for occidental sources with this new terminology.

Read this paper on arXiv…

V. Carrasco, R. Trigo and J. Vaquero
Mon, 22 May 17

Comments: 6 pages, accepted for publication in Publ. Astron. Soc. Jpn

Photometric and spectroscopic variability of the B5IIIe star HD 171219 [SSA]


We analyzed the star HD 171219, one of the relatively bright Be stars observed in the seismo field of the CoRoT satellite, in order to determine its physical and pulsation characteristics. Classical Be stars are main-sequence objects of mainly B-type, whose spectra show, or had shown at some epoch, Balmer lines in emission and an infrared excess. Both characteristics are attributed to an equatorially concentrated circumstellar disk fed by non-periodic mass-loss episodes (outbursts). Be stars often show nonradial pulsation gravity modes and, as more recently discovered, stochastically excited oscillations. Applying the CLEANEST algorithm to the high-cadence and highly photometrically precise measurements of the HD 171219 light curve led us to perform an unprecedented detailed analysis of its nonradial pulsations. Tens of frequencies have been detected in the object compatible with nonradial g-modes. Additional high-resolution ground-based spectroscopic observations were obtained at La Silla (HARPS) and Haute Provence (SOPHIE) observatories during the month preceding CoRoT observations. Additional information was obtained from low-resolution spectra from the BeSS database. From spectral line fitting we determined physical parameters of the star, which is seen equator-on. We also found in the ground data the same frequencies as in CoRoT data. Additionally, we analyzed the circumstellar activity through the traditional method of V/R emission H{\alpha} line variation. A quintuplet was identified at approximately 1.113 c/d (12.88 {\mu}Hz) with a separation of 0.017 c/d that can be attributed to a pulsation degree l~2. The light curve shows six small- to medium-scale outbursts during the CoRoT observations. The intensity of the main frequencies varies after each outburst, suggesting a possible correlation between the nonradial pulsations regime and the feeding of the envelope.

Read this paper on arXiv…

L. Andrade, E. Janot-Pacheco, M. Emilio, et. al.
Mon, 22 May 17

Comments: 7 pages, 10 figures

Isochrones of M67 with an Expanded Set of Parameters [SSA]


We create isochrones of M67 using the Yale Rotating Stellar Evolution Code. In addition to metallicity, parameters that are traditionally held fixed, such as the mixing length parameter and initial helium abundance, also vary. The amount of convective overshoot is also changed in different sets of isochrones. Models are constructed both with and without diffusion. From the resulting isochrones that fit the cluster, the age range is between 3.6 and 4.8 Gyr and the distance is between 755 and 868 pc. We also confirm Michaud et al. (2004) claim that M67 can be fit without overshoot if diffusion is included.

Read this paper on arXiv…

L. Viani and S. Basu
Mon, 22 May 17

Comments: 4 pages, 3 figures, to appear in the proceedings of the joint TASC2/KASC9/SPACEINN/HELAS8 conference “Seismology of the Sun and the Distant Stars 2016”

New Cataclysmic Variables and other Exotic Binaries in the Globular Cluster 47 Tucanae [SSA]


We present 22 new (+3 confirmed) cataclysmic variables (CVs) in the non core-collapsed globular cluster 47 Tucanae (47 Tuc). The total number of CVs in the cluster is now 43, the largest sample in any globular cluster so far. For the identifications we used near-ultraviolet (NUV) and optical images from the Hubble Space Telescope, in combination with X-ray results from the Chandra X-ray Observatory. This allowed us to build the deepest NUV CV luminosity function of the cluster. We found that the CVs in 47 Tuc are more concentrated towards the cluster center than the main sequence turnoff stars. We compared our results to the CV populations of the core-collapsed globular clusters NGC 6397 and NGC 6752. We found that 47 Tuc has fewer bright CVs per unit mass than those two other clusters. That suggests that dynamical interactions in core-collapsed clusters play a major role creating new CVs. In 47 Tuc, the CV population is probably dominated by primordial and old dynamically formed systems. We estimated that the CVs in 47 Tuc have total masses of approx. 1.4 M_sun. We also found that the X-ray luminosity function of the CVs in the three clusters is bimodal. Additionally, we discuss a possible double degenerate system and an intriguing/unclassified object. Finally, we present four systems that could be millisecond pulsar companions given their X-ray and NUV/optical colors. For one of them we present very strong evidence for being an ablated companion. The other three could be CO- or He-WDs.

Read this paper on arXiv…

L. Sandoval, M. Berg, C. Heinke, et. al.
Mon, 22 May 17

Comments: Submitted to MNRAS. 29 Pages, 20 Figures, 5 Tables

Solar cycle indices from the photosphere to the corona: measurements and underlying physics [SSA]


A variety of indices have been proposed in order to represent the many different observables modulated by the solar cycle. Most of these indices are highly correlated with each other owing to their intrinsic link with the solar magnetism and the dominant eleven year cycle, but their variations may differ in fine details, as well as on short- and long-term trends. In this paper we present an overview of the indices that are often employed to describe the many features of the solar cycle, moving from the ones referring to direct observations of the inner solar atmosphere, the photosphere and chromosphere, to those deriving from measurements of the transition region and solar corona. For each index, we summarize existing measurements {\bf and typical use}, and for those that quantify physical observables, we describe the underlying physics.

Read this paper on arXiv…

I. Ermolli, K. Shibasaki, A. Tlatov, et. al.
Mon, 22 May 17

Comments: N/A

X-Ray Superflares on CC Eri [SSA]


We present an in-depth study of two superflares (F1 and F2) detected on an active binary star CC Eridani by the Swift observatory. These superflares triggered the Burst Alert Telescope (BAT) in the hard X-ray band on 2008 October 16 and 2012 February 24. The rise phases of both the flares were observed only with BAT, whereas the decay phases were observed simultaneously with the X-ray Telescope. It has been found that the flares decay faster in the hard X-ray band than in the soft X-ray band. Both flares F1 and F2 are highly energetic with respective peak X-ray luminosities of $\sim$$10^{32.2}$ and $\sim$$10^{31.8}$ erg s$^{-1}$ in 0.3–50 keV energy band, which are larger than any other flares previously observed on CC Eri. The time-resolved spectral analysis during the flares shows the variation in the coronal temperature, emission measure, and abundances. The elemental abundances are enhanced by a factor of $\sim$8 to the minimum observed in the post-flare phase for the flare F1. The observed peak temperatures in these two flares are found to be 174 MK and 128 MK. Using the hydrodynamic loop modeling, we derive loop lengths for both the flares as 1.2$\pm$0.1$\times$10$^{10}$ cm and 2.2$\pm$0.6$\times$10$^{10}$ cm, respectively. The Fe K$\alpha$ emission at 6.4 keV is also detected in the X-ray spectra and we model the K$\alpha$ emission feature as fluorescence from the hot flare source irradiating the photospheric iron. These superflares are the brightest, hottest, and shortest in duration observed thus far on CC Eri.

Read this paper on arXiv…

S. Karmakar, J. Pandey, V. Airapetian, et. al.
Mon, 22 May 17

Comments: N/A

Stellar Parameters in an Instant with Machine Learning: Application to Kepler LEGACY Targets [SSA]


With the advent of dedicated photometric space missions, the ability to rapidly process huge catalogues of stars has become paramount. Bellinger and Angelou et al. (2016) recently introduced a new method based on machine learning for inferring the stellar parameters of main-sequence stars exhibiting solar-like oscillations. The method makes precise predictions that are consistent with other methods, but with the advantages of being able to explore many more parameters while costing practically no time. Here we apply the method to 52 so-called “LEGACY” main-sequence stars observed by the Kepler space mission. For each star, we present estimates and uncertainties of mass, age, radius, luminosity, core hydrogen abundance, surface helium abundance, surface gravity, initial helium abundance, and initial metallicity as well as estimates of their evolutionary model parameters of mixing length, overshooting coefficient, and diffusion multiplication factor. We obtain median uncertainties in stellar age, mass, and radius of 14.8%, 3.6%, and 1.7%, respectively.
The source code for all analyses and for all figures appearing in this manuscript can be found electronically at: https://github.com/earlbellinger/asteroseismology

Read this paper on arXiv…

E. Bellinger, G. Angelou, S. Hekker, et. al.
Mon, 22 May 17

Comments: 4 pages, 3 figures, 2 tables, to appear in the proceedings of the joint TASC2/KASC9/SPACEINN/HELAS8 conference “Seismology of the Sun and the Distant Stars 2016”