Convection structure in the solar photosphere at granulation and mesogranulation scales

Baran, O. A.; Stodilka, M. I.

doi:10.3103/s0884591315020026

Cited by 12 publications

(5 citation statements)

References 15 publications

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“…Calculated across all maps, Θ RMS = 0.0457 (or ±260 K from the mean in absolute terms). Our value is slightly higher than some literature values (see Puschmann et al 2005;Baran & Stodilka 2015;Gray & Oostra 2018), which typically note 150 − 200 K variations from the mean in photospheric temperatures. However, we note that Beck et al (2013) present measurements of temperature fluctuations in solar simulations which are comparable to our values, as well as measurements of observational temperature fluctuations more comparable to the literature values noted previously, and they show that the simulations, when degraded with an appropriate PSF and modeled stray-light contribution, closely match the observational values.…”

Section: Discussioncontrasting

confidence: 76%

Magnetic Activity of F-, G-, and K-type Stars in the LAMOST–Kepler Field

Zhang

et al. 2020

ApJS

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Monitoring chromospheric and photospheric indexes of magnetic activity can provide valuable information, especially the interaction between different parts of the atmosphere and their response to magnetic fields. We extract chromospheric indexes, S and + R HK , for 59,816 stars from LAMOST spectra in the LAMOST-Kepler program, and photospheric index, R eff , for 5575 stars from Kepler light curves. The log R eff shows positive correlation with log + R HK . We estimate the power-law indexes between R eff and + R HK for F-, G-, and K-type stars, respectively. We also confirm the dependence of both chromospheric and photospheric activity on stellar rotation. Ca II H and K emissions and photospheric variations generally decrease with increasing rotation periods for stars with rotation periods exceeding a few days. The power-law indexes in exponential decay regimes show different characteristics in the two activity-rotation relations. The updated largest sample including the activity proxies and reported rotation periods provides more information to understand the magnetic activity for cool stars.

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Section: Discussioncontrasting

confidence: 76%

Magnetic Activity of F-, G-, and K-type Stars in the LAMOST–Kepler Field

Zhang

et al. 2020

ApJS

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“…Doppler images obtained in the core of this line show that the granulation structure still exists, but it differs markedly from the granulation pattern seen in the wings of this line [41]. According to [8,30], the structure of granulation is preserved up to heights of approximately 500-700 km, while its characteristics vary with height. The temperature inversion in granules and intergranules almost always occurs, on average, at heights of 200-300 km, while the inversion of vertical velocities occurs in most cases at heights > 500 km.…”

Section: Line Bisectors In the Solar Flux Spectrummentioning

confidence: 81%

“…Íà äîïïëåðîãðàìàõ, îòðèìàíèõ â ÿäð³ ö³º¿ ë³í³¿, âèäíî, ùî ãðàíóëÿö³éíà ñòðóêòóðà ùå ïðîÿâëÿºòüñÿ, àëå âîíà çíà÷íî â³äð³çíÿºòüñÿ â³ä êàðòèíè ãðàíóëÿ -ö³¿, âèäèìî¿ â êðèëàõ ö³º¿ ë³í³¿ [41]. Çã³äíî ç äàíèìè [8,30] ñòðóêòóðà ãðàíóëÿö³¿ çáåð³ãàºòüñÿ äî âèñîò áëèçüêî 500...700 êì, ïðè öüîìó ¿¿ õàðàêòåðèñòèêè çì³íþþòüñÿ ç âèñîòîþ. Ó ãðàíóëàõ ³ ì³aeãðàíóëàõ ìàé aeå çàâaeäè â³äáóâàºòüñÿ ³íâåðñ³ÿ òåìïåðàòóðè â ñåðåäíüîìó íà âèñîòàõ 200…300 êì, òîä³ ÿê ³íâåðñ³ÿ âåðòèêàëüíèõ øâèäêîñòåé â³äáóâàºòüñÿ ó á³ëüøîñò³ âèïàäê³â íà âèñîòàõ íå íèae÷å 500 êì.…”

Section: á²ñåêòîðè ë²í²é ó ñïåêòð² ñîíß×íîãî ïîòîêóunclassified

The line asymmetry in the spectra of the Sun and solar-type stars

Sheminova¹

2020

Kinemat. fiz. nebesnyh tel (Online)

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We have analysed the asymmetry of lines Fe I and Fe II in spectra of a solar flux using three FTS atlases and the HARPS atlas and also in spectra of 13 stars using observation data on the HARPS spectrograph. To reduce observation noise individual line bisectors of each star have been averaged. The obtained average bisectors in the stellar spectra are more or less similar to the shape C well known to the Sun. In stars with rotation velocities greater than 5 km/s the shape of the bisectors is more like /. The curvature and span of the bisectors increase with the temperature of the star. Our results confirm the known facts about strong influence of rotation velocity on the span and shape of bisectors. The average convective velocity was determined based on the span of the average bisector, which shows the largest difference between the velocity of cold falling and hot rising convective flows of the matter. It’s equal to -420 m/s for the Sun as a star. In stars, it grows from -150 to -700 m/s with an effective temperature of 4800 to 6200 K, respectively. For stars with greater surface gravity and greater metallicity, the average convective velocity decreases. It also decreases with star age and correlates with the velocity of micro and macroturbulent movements. The results of solar flux analysis showed that absolute wavelength scales in the atlases used coincide with an accuracy of about -10 m/s, except for the FTS-atlas of Hinkle et al., whose scale is shifted and depends on the wavelength. In the range from 450 to 650 nm, the scale shift of this atlas varies from -100 to -330 m/s, respectively, and it equals on average of 240 m/s. The resulting average star bisectors contain information about the fields of convective velocities and may be useful for hydrodynamic modeling of stellar atmospheres in order to study the characteristic features of surface convection.

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“…A deeper understanding of the character of the height dependences of convective velocities is given by the results of studying granulation in quiet regions of the Sun with a high spatial resolution (approximately 0.5 ). It was shown in a number of studies [6,19,57] that temperature inversion in granules and intergranules occurs at heights of 200-300 km and higher. These are the heights at which the height dependences of the shifts we obtained deviate from the linear dependence.…”

Section: Resultsmentioning

confidence: 99%

“…These are the heights at which the height dependences of the shifts we obtained deviate from the linear dependence. According to the data in [6], the pattern of the processes of granulation is as follows. The substance of the central parts of the granules becomes colder at these heights and continues to move upward.…”

Section: Resultsmentioning

confidence: 99%

Convective Line Shifts in the Spectra of Solar-Type Stars

Sheminova

2022

Preprint

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The Doppler line shifts in the spectra of the Sun and stars with effective temperatures from 4800 to 6200 K were measured and the average connective (granulation) velocities were estimated. The absolute scale of the line shifts for the stars was established on the basis of the derived dependence of the shifts of solar lines on optical depth. For FGK solar-type stars, curves of convection velocities as a function of the height in the atmosphere in a large range of heights from 150 to 700 km were obtained for the first time. All these curves indicate a decrease in blue shifts with height, which means that the granulation velocities through the photosphere slow down to zero. In the lower chromosphere, red shifts of strong Mg I lines are observed, which indicate a change in the direction of granulation velocities to the opposite and confirm the effects of reversal of granulation at heights above 600 km. In cooler K stars, granulation shifts change with height on average from −50 to 100 m/s, while they change more sharply in hotter FG stars from −700 to 300 m/s. The gradient of the line shift curves increases with an increase in the effective temperature and a decrease in gravity, metallicity, and age of the star. The connective velocity of the star averaged over all analyzed heights increases from −90 to −560 m/s from colder to hotter stars. It correlates with macroturbulence, asymmetry of spectral lines, and the rotation velocity of the star. We also obtained the radial velocities of the stars and compared them with the SIMBAD data. Large deviations of −21050 and 1775 m/s were found for the stars HD 102361 and HD 42936, respectively. For the rest of the stars, the deviation does not exceed ±340 m/s, which is probably associated with the use of an average granulation velocity of −300 m/s in the SIM-BAD data. Our analysis has shown that the average granulation velocity is not the same for solar-type stars. It is lower in colder stars and higher in hotter stars than the Sun. Therefore, determination of the radial velocities needs to take into account the individual granulation velocities of stars.

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Convection structure in the solar photosphere at granulation and mesogranulation scales

Cited by 12 publications

References 15 publications

Magnetic Activity of F-, G-, and K-type Stars in the LAMOST–Kepler Field

Magnetic Activity of F-, G-, and K-type Stars in the LAMOST–Kepler Field

The line asymmetry in the spectra of the Sun and solar-type stars

Convective Line Shifts in the Spectra of Solar-Type Stars

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