Context. The Kepler spacecraft is providing time series of photometric data with micromagnitude precision for hundreds of A-F type stars. Aims. We present a first general characterization of the pulsational behaviour of A-F type stars as observed in the Kepler light curves of a sample of 750 candidate A-F type stars, and observationally investigate the relation between γ Doradus (γ Dor), δ Scuti (δ Sct), and hybrid stars. Methods. We compile a database of physical parameters for the sample stars from the literature and new ground-based observations. We analyse the Kepler light curve of each star and extract the pulsational frequencies using different frequency analysis methods. We construct two new observables, “energy ”a nd “efficiency”, related to the driving energy of the pulsation mode and the convective efficiency of the outer convective zone, respectively. Results. We propose three main groups to describe the observed variety in pulsating A-F type stars: γ Dor, δ Sct, and hybrid stars. We assign 63% of our sample to one of the three groups, and identify the remaining part as rotationally modulated/active stars, binaries, stars of different spectral type, or stars that show no clear periodic variability. 23% of the stars (171 stars) are hybrid stars, which is a much higher fraction than what has been observed before. We characterize for the first time a large number of A-F type stars (475 stars) in terms of number of detected frequencies, frequency range, and typical pulsation amplitudes. The majority of hybrid stars show frequencies with all kinds of periodicities within the γ Dor and δ Sct range, also between 5 and 10 d −1 , which is a challenge for the current models. We find indications for the existence of δ Sct and γ Dor stars beyond the edges of the current observational instability strips. The hybrid stars occupy the entire region within the δ Sct and γ Dor instability strips and beyond. Non-variable stars seem to exist within the instability strips. The location of γ Dor and δ Sct classes in the (Teff ,l ogg)-diagram has been extended. We investigate two newly constructed variables, “efficiency ”a nd “energy”, as a means to explore the relation between γ Dor and δ Sct stars. Conclusions. Our results suggest a revision of the current observational instability strips of δ Sct and γ Dor stars and imply an investigation of pulsation mechanisms to supplement the κ mechanism and convective blocking effect to drive hybrid pulsations. Accurate physical parameters for all stars are needed to confirm these findings.

/pdf/the-kepler-characterization-of-the-variability-among-a-and-f-y9gptafczn.pdf

The Kepler characterization of the variability among A- and F-type stars I. General overview

The Kepler spacecraft is providing time series of photometric data with micromagnitude precision for hundreds of A-F type stars. We present a first general characterization of the pulsational behaviour of A-F type stars as observed in the Kepler light curves of a sample of 750 candidate A-F type stars. We propose three main groups to describe the observed variety in pulsating A-F type stars: gamma Dor, delta Sct, and hybrid stars. We assign 63% of our sample to one of the three groups, and identify the remaining part as rotationally modulated/active stars, binaries, stars of different spectral type, or stars that show no clear periodic variability. 23% of the stars (171 stars) are hybrid stars, which is a much larger fraction than what has been observed before. We characterize for the first time a large number of A-F type stars (475 stars) in terms of number of detected frequencies, frequency range, and typical pulsation amplitudes. The majority of hybrid stars show frequencies with all kinds of periodicities within the gamma Dor and delta Sct range, also between 5 and 10 c/d, which is a challenge for the current models. We find indications for the existence of delta Sct and gamma Dor stars beyond the edges of the current observational instability strips. The hybrid stars occupy the entire region within the delta Sct and gamma Dor instability strips, and beyond. Non-variable stars seem to exist within the instability strips. The location of gamma Dor and delta Sct classes in the (Teff,logg)-diagram has been extended. We investigate two newly constructed variables 'efficiency' and 'energy' as a means to explore the relation between gamma Dor and delta Sct stars. Our results suggest a revision of the current observational instability strips, and imply an investigation of other pulsation mechanisms to supplement the kappa mechanism and convective blocking effect to drive hybrid pulsations.

/pdf/the-kepler-characterization-of-the-variability-among-a-and-f-2au724c8rd.pdf

The Kepler characterization of the variability among A- and F-type stars. I. General overview

In this paper we describe a new class of pulsating stars, the prototype of which is the bright, early, F‐type dwarf γ Doradus These stars typically have between 1 and 5 periods ranging from 04 to 3 days with photometric amplitudes up to 01 mag in Johnson V The mechanism for these observed variations is high‐order, low‐degree, nonradial, gravity‐mode pulsation

https://iopscience.iop.org/article/10.1086/316399/pdf

γ Doradus Stars: Defining a New Class of Pulsating Variables

In this paper we describe a new class of pulsating stars, the prototype of which is the bright, early, F-type dwarf, Gamma Doradus. These stars typically have between 1 and 5 periods ranging from 0.4 to 3 days with photometric amplitudes up to 0.1 in Johnson V. The mechanism for these observed variations is high-order, low-degree, non-radial, gravity-mode pulsation. Gamma Doradus stars exhibit variability on a time scale that is an order of magnitude slower than Delta Scuti stars. They may offer additional insight into stellar physics when they are better understood (e.g., they may represent the cool portion of an "iron opacity instability strip" currently formed by the Beta Cephei stars, the SPB stars, and the subdwarf B stars; they may also offer insight into the presence of g-modes in solar-like stars).

Gamma Doradus Stars: Defining a New Class of Pulsating Variables

We present new high-dispersion spectroscopic and precise photometric observations to identify 11 new γ Doradus variables Seven of these new γ Doradus stars appear to be single, three are primaries of single-lined binaries, and one has two distant visual companions; none are double-lined or close visual binaries Several of the stars show spectroscopic line-profile and low-amplitude radial velocity variability indicative of pulsation All 11 stars are photometrically variable with amplitudes between 8 and 93 mmag in Johnson B and periods between 0398 and 2454 days One star is monoperiodic; the rest have between two and five independent periods The variability at all periods approximates a sinusoid, although three of the stars exhibit cycle-to-cycle variation in the level of maximum brightness, similar to the Blazhko effect observed in some RR Lyrae stars We provide a new tabulation of all 54 γ Doradus stars confirmed to date and list some of their properties All are dwarfs or subgiants and lie within a well-defined region of the H-R diagram that overlaps the cool edge of the δ Scuti instability strip Four of the new γ Doradus variables from this paper also lie within the δ Scuti instability strip but do not exhibit the additional higher frequency variability typical of δ Scuti stars The variability type of several of these stars given in the General Catalog of Variable Stars and in SIMBAD should now be revised

/pdf/eleven-new-g-doradus-stars-1pcwr4i5a4.pdf

Eleven New γ Doradus Stars

Untuk menyiasati hal ini, biasanya petani terus menambah jumlah pupuk kimia yang akan diaplikasikan ke tanaman, yang justru mengakibatkan kondisi tanah semakin kritis. Akibatnya, dari tahun ke tahun penggunaan pupuk kimia semakin bertambah. Hal ini tentu saja menambah beban biaya bagi petani. Untuk itu, saat ini pemerintah giat mensosialisasikan penggunaan pupuk organik, yaitu pupuk yang terbuat dari bahan-bahan organik (sisa-sisa makhluk hidup) dengan kandungan unsur hara yang terkandung secara alami yang disebut Kompos. Kompos dikenal pula dengan nama bokashi, yang merupakan singkatan dari Bahan Organik Kaya Sumber Hayati.

BOKASHI, “Bahan Organik Kaya Akan Sumber Hayati’

/pdf/the-g-dor-variable-hd-164615-results-from-a-multisite-47a0r3wxkm.pdf

The γ Dor variable HD 164615: results from a multisite photometric campaign

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BOKASHI, “Bahan Organik Kaya Akan Sumber Hayati’

The γ Dor variable HD 164615: results from a multisite photometric campaign