Asteroseismology of 16000 Kepler Red Giants: Global Oscillation Parameters, Masses, and Radii

The Kepler mission has provided exquisite data to perform an ensemble asteroseismic analysis on evolved stars. In this work we systematically characterize solar-like oscillations and granulation for 16,094 oscillating red giants, using end-of-mission long-cadence data. We produced a homogeneous catalog of the frequency of maximum power (typical uncertainty $\sigma_{\nu_{\rm max}}$=1.6\%), the mean large frequency separation ($\sigma_{\Delta\nu}$=0.6\%), oscillation amplitude ($\sigma_{\rm A}$=4.7\%), granulation power ($\sigma_{\rm gran}$=8.6\%), power excess width ($\sigma_{\rm width}$=8.8\%), seismically-derived stellar mass ($\sigma_{\rm M}$=7.8\%), radius ($\sigma_{\rm R}$=2.9\%), and thus surface gravity ($\sigma_{\log g}$=0.01 dex). Thanks to the large red giant sample, we confirm that red-giant-branch (RGB) and helium-core-burning (HeB) stars collectively differ in the distribution of oscillation amplitude, granulation power, and width of power excess, which is mainly due to the mass difference. The distribution of oscillation amplitudes shows an extremely sharp upper edge at fixed $\nu_{\rm max}$, which might hold clues to understand the excitation and damping mechanisms of the oscillation modes. We find both oscillation amplitude and granulation power depend on metallicity, causing a spread of 15\% in oscillation amplitudes and a spread of 25\% in granulation power from [Fe/H]=-0.7 to 0.5 dex. Our asteroseismic stellar properties can be used as reliable distance indicators and age proxies for mapping and dating galactic stellar populations observed by Kepler. They will also provide an excellent opportunity to test asteroseismology using Gaia parallaxes, and lift degeneracies in deriving atmospheric parameters in large spectroscopic surveys such as APOGEE and LAMOST.Comment: Accepted for publication in ApJS. Both table 1 and 2 are available for download as ancillary file

Finding non-eclipsing binaries through pulsational phase modulation

We present a method for finding binaries among pulsating stars that were observed by the Kepler Mission. We use entire four-year light curves to accurately mea- sure the frequencies of the strongest pulsation modes, then track the pulsation phases at those frequencies in 10-d segments. This produces a series of time-delay measurements in which binarity is apparent as a periodic modulation whose amplitude gives the projected light travel time across the orbit. Fourier analysis of this time-delay curve provides the pa- rameters of the orbit, including the period, eccentricity, angle of ascending node and time of periastron passage. Differentiating the time-delay curve yields the full radial-velocity curve directly from the Kepler photometry, without the need for spectroscopy. We show examples with delta Scuti stars having large numbers of pulsation modes, including one system in which both components of the binary are pulsating. The method is straightfor- ward to automate, thus radial velocity curves can be derived for hundreds of non-eclipsing binary stars from Kepler photometry alone. This contribution is based largely upon the work by Murphy et al. [1], describing the phase-modulation method in detail

Digitaalisen opetuksen kasvuyritysten kansainvälistymiseen vaikuttavat tekijät

As well as many other industries, education is currently being disrupted by new emerging digital solutions. Teachers all around the world are adopting new digital materials to their everyday teaching including digital books and educational games. This recent trend engenders opportunity for new companies to emerge with cutting-edge digital educational solutions. Furthermore, with a digital solution expansion to international markets without heavy investments is possible. However, for example in Finland only few companies have been able to successfully enter new markets with educational technology. Internationalization strategies have been widely studied during the past few decades. The early studies already identified a set of different market entry modes including export, licensing, franchising, joint ventures and wholly-owned subsidiaries. However, for small resource-limited companies, export is the most viable option. Export allows company to maintain the full control of the process and product without making heavy investments on the internationalization. The export performance framework shows that the export strategy is depending on both internal (company resources) and external factors (country and industry characteristics). More recent studies have also identified alternative entry modes such as cooperative strategies and innovative use of internet. However, the previous literature has not studied this topic purely in education industry and therefore does not provide detailed knowledge for startups planning international expansion in digital education industry. The aim of this study is to identify key determinants for market entry strategy selection for startups in digital education, and identify different strategies for addressing the major challenges in the digital education markets. To study this topic, 15 interviews were carried out to both experts of internationalization of digital education and companies that are pursuing international expansion with digital educational solutions. The data analysis followed Gioia methodology (Gioia, Corley, & Hamilton, 2012), in which 1st-order terms are identified first, and then the 2nd-order themes are established accordingly. The findings revealed several market-level factors that drive the market entry strategy selection. These factors were related to cultural and regulatory differences, trust and reliability, different customer types and customer needs. In addition, the findings showed several strategies how companies can address the challenges related to the above market-level factors. Therefore, this study provides managers of startups with insights of digital education markets as well as a toolkit for addressing the market-level challenges in digital education.Opetusala on kokemassa suuria muutoksia uusien digitaalisten ratkaisuiden myötä. Opettajat ympäri maailmaa ottavat opetuskäyttöön uusia digitaalisia ratkaisuja kuten digitaalisia oppikirjoja sekä oppimispelejä. Opetuksen digitalisaatio synnyttää uusia yrityksiä, jotka tuottavat innovatiivisia ja moderneja teknologiaratkaisuja opetuskäyttöön. Tämänlaisille digitaalisia ratkaisuja tuottaville yrityksille on mahdollista myös kasvaa kansainvälisesti ilman suuria alkuinvestointeja. Kuitenkin vain muutama suomalainen digitaalisia ratkaisuja tuottava yritys on kyennyt onnistuneesti laajentumaan uusille markkinoille. Kansainvälistymisstrategioita on tutkittu laajalti viimeisten vuosikymmenien aikana. Jo aikaiset tutkimukset määrittelivät erilaisia tapoja tunkeutua uusille markkinoille. Näitä tapoja ovat muun muassa vienti, lisensointi, franchise-periaate, yhteisyritys sekä tytäryhtiö. Useimmille pienille yrityksille suora vienti on kuitenkin parhaiten sopiva tapa kansainvälistyä. Suora vienti antaa yritykselle täyden kontrollin operaatiosta ja tuotteesta vaatimatta kuitenkaan suuria alkuinvestointeja. Viennin suorituskyky –malli osoittaa, että vientistrategia perustuu sekä sisäisiin (yrityksen resurssit) että ulkoisiin tekijöihin (markkina- ja toimiala kohtaisiin tekijöihin). Uudemmat tutkimukset ovat lisäksi esittäneet vaihtoehtoisia tapoja tunkeutua markkinoille kuten yhteistyöhön perustuvat strategiat ja internetin innovatiivinen hyödyntäminen. Kirjallisuus ei kuitenkaan ole tutkinut kansainvälistymistä pelkästään opetusalan näkökulmasta, eikä täten tarjoa yksityiskohtaista tietoa pienten digitaalisia ratkaisuja tuottavan yrityksen kansainvälistymisestä. Tämän tutkimuksen tavoitteena on tunnistaa keskeisimmät tekijät, jotka vaikuttavat pienten kasvuyritysten tapaan tunkeutua markkinoille, sekä tunnistaa erilaisia strategioita markkinoiden keskeisimpien haasteiden ylittämiseen. Tutkimuksessa suoritettiin 15 haastattelua sekä opetuksen kansainvälistämisen eksperteille että pienille kasvuyrityksille, jotka ovat kansainvälistyneet digitaalisen opetuksen alalla. Haastatteludata analysoitiin käyttämällä Gioia-metodia (Gioia et al., 2012), jossa tunnistetaan ensin ensimmäisen tason aiheet, joiden perusteella voidaan luoda laajempia toisen tason teemoja. Tutkimuksen tulokset toivat ilmi useita markkina-tason tekijöitä, jotka vaikuttavat yrityksen tapaan tunkeutua markkinoille. Nämä tekijät liittyivät kulttuuriin ja sääntelyyn, luotettavuuteen, erilaisiin asiakastyyppeihin, sekä asiakkaiden tarpeisiin. Tulokset toivat esiin myös useita tapoja, joilla yritykset voivat ylittää keskeiset haasteet liittyen edellä mainittuihin markkina-tason tekijöihin. Tutkimuksen tulokset tuovat esiin markkinoiden keskeisiä piirteitä sekä erilaisia tapoja vastata markkinoiden erityispiirteistä syntyviin haasteisiin

A grid of 800,000 models of delta Scuti stars using MESA and GYRE

The rapidly increasing number of delta Scuti stars with regular patterns among their pulsation frequencies necessitates modelling tools to better understand the observations. Further, with a dozen identified modes per star, there is potential to make meaningful inferences on stellar structure using these young $\delta$ Sct stars. We compute and describe a grid of $>$800,000 stellar models from the early pre-main-sequence to roughly one third of the main-sequence lifetime, and calculate their pulsation frequencies. From these, we also calculate asteroseismic parameters and explore how those parameters change with mass, age, and metal mass fraction. We show that the large frequency separation, $\Delta\nu$, is insensitive to mass at the zero-age main sequence. In the frequency regime observed, the $\Delta\nu$ we measure (from modes with $n\sim5$--9) differs from the solar scaling relation by $\sim$13%. We find that the lowest radial order is often poorly modelled, perhaps indicating that the lower-order pressure modes contain further untapped potential for constraining the stellar structure. We also show that different nuclear reaction networks available in MESA can affect the pulsation frequencies of young $\delta$ Sct stars by as much as 5%. We apply the grid to five newly modelled stars, including two pre-main-sequence stars each with 15+ modes identified, and we make the grid available as a community resource.Comment: 17 pages including appendices. Submitted to MNRA

The Kepler Smear Campaign: Light curves for 102 Very Bright Stars

We present the first data release of the Kepler Smear Campaign, using collateral 'smear' data obtained in the Kepler four-year mission to reconstruct light curves of 102 stars too bright to have been otherwise targeted. We describe the pipeline developed to extract and calibrate these light curves, and show that we attain photometric precision comparable to stars analyzed by the standard pipeline in the nominal Kepler mission. In this paper, aside from publishing the light curves of these stars, we focus on 66 red giants for which we detect solar-like oscillations, characterizing 33 of these in detail with spectroscopic chemical abundances and asteroseismic masses as benchmark stars. We also classify the whole sample, finding nearly all to be variable, with classical pulsations and binary effects. All source code, light curves, TRES spectra, and asteroseismic and stellar parameters are publicly available as a Kepler legacy sample.Comment: 35 pages, accepted ApJ

E´ chelle diagrams and period spacings of g modes in: Doradus stars from four years of Kepler observations

We use photometry from the Kepler Mission to study oscillations in Doradus stars. Some stars show remarkably clear sequences of g modes and we use period ´echelle diagrams to measure period spacings and identifyrotationally split multiplets with ` = 1 and ` = 2.We find small deviations from regular period spacings that arise from the gradient in the chemical composition just outside the convective core. We also find stars for which the period spacing shows a strong linear trend as a function of period, consistent with relatively rapid rotation. Overall, th

Finding binaries from phase modulation of pulsating stars with \textit{Kepler}: VI. Orbits for 10 new binaries with mischaracterised primaries

Measuring phase modulation in pulsating stars has proved to be a highly successful way of finding binary systems. The class of pulsating main-sequence A and F variables known as delta Scuti stars are particularly good targets for this, and the \textit{Kepler} sample of these has been almost fully exploited. However, some \textit{Kepler} $\delta$ Scuti stars have incorrect temperatures in stellar properties catalogues, and were missed in previous analyses. We used an automated pulsation classification algorithm to find 93 new $\delta$ Scuti pulsators among tens of thousands of F-type stars, which we then searched for phase modulation attributable to binarity. We discovered 10 new binary systems and calculated their orbital parameters, which we compared with those of binaries previously discovered in the same way. The results suggest that some of the new companions may be white dwarfs.Comment: 8 pages, 6 figures that make liberal use of colou

TESS observations of the Pleiades cluster: a nursery for delta Scuti stars

We studied 89 A- and F-type members of the Pleiades open cluster, including five escaped members. We measured projected rotational velocities (v sin i) for 49 stars and confirmed that stellar rotation causes a broadening of the main sequence in the color-magnitude diagram. Using time-series photometry from NASA's TESS Mission (plus one star observed by Kepler/K2), we detected delta Scuti pulsations in 36 stars. The fraction of Pleiades stars in the middle of the instability strip that pulsate is unusually high (over 80%), and their range of effective temperatures agrees well with theoretical models. On the other hand, the characteristics of the pulsation spectra are varied and do not correlate with stellar temperature, calling into question the existence of a useful nu_max relation for delta Scutis, at least for young stars. By including delta Scuti stars observed in the Kepler field, we show that the instability strip is shifted to the red with increasing distance by interstellar reddening. Overall, this work demonstrates the power of combining observations with Gaia and TESS for studying pulsating stars in open clusters.Comment: submitted to AAS journal

Mortality of Cranes (Gruidae) Associated with Powerlines over a Major Roost on the Platte River, Nebraska

Two 69-kilovolt powerlines spanning the Platte River in south central Nebraska are suspected to cause substantial mortality to sandhill cranes (Grus canadensis) and pose a threat to endangered whooping cranes (G. americana) that roost overnight on the river during spring and fall migrations. Most studies of crane collisions with powerlines in the region have focused on counts of carcasses away from night roosts on the river and none have accounted for potential biases in detecting carcasses. We found 61 carcasses of sandhill cranes below over-river segments of the two powerlines during 4 March to 7 April 2006 and 90 such carcasses between 5 March and 13 April 2007. In 2007 we estimated the number of carcasses undetected in our surveys due to removal by scavengers, loss to downstream flow, and observer oversight. We estimated between 165 and 219 sandhill cranes were killed by the two powerlines during spring 2007. These cnlculations exclude mortalities from individuals injured by powerline collisions and dying elsewhere, as well as those killed before or after our 5 March to 13 April survey period. We detected no evidence of mortality for whooping cranes during our surveys. Our results corroborate anecdotal evidence of signficant sandhill crane mortality each spring due to collisions with above-ground powerlines at this major night roost. Collisions by sandhill cranes will continue and collisions by Whooping cranes seem likely unless an effective means of averting birds from powerlines is implemented at this site