Savita Mathur - Academia.edu (original) (raw)

Papers by Savita Mathur

HAL (Le Centre pour la Communication Scientifique Directe), Oct 1, 2011

More than 1000 red giants have been observed by NASA/Kepler mission during a nearly continuous pe... more More than 1000 red giants have been observed by NASA/Kepler mission during a nearly continuous period of ∼ 13 months. The resulting high-frequency resolution (< 0.03 µHz) allows us to study the granulation parameters of these stars. The granulation pattern results from the convection motions leading to upward flows of hot plasma and downward flows of cooler plasma. We fitted Harvey-like functions to the power spectra, to retrieve the timescale and amplitude of granulation. We show that there is an anti-correlation between both of these parameters and the position of maximum power of acoustic modes, while we also find a correlation with the radius, which agrees with the theory. We finally compare our results with 3D models of the convection.

The Astronomical Journal, 2020

A-970. Based on observations obtained with the Nordic Optical Telescope (NOT), operated on the is... more A-970. Based on observations obtained with the Nordic Optical Telescope (NOT), operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos (ORM) of the Instituto de Astrofísica de Canarias (IAC). This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. This work makes use of observations from the LCOGT network.

The Astrophysical Journal, 2020

We use models of stellar angular momentum evolution to determine ages for ∼ 500 stars in the APOG... more We use models of stellar angular momentum evolution to determine ages for ∼ 500 stars in the APOGEE-Kepler Cool Dwarfs sample. We focus on lower main-sequence stars, where other age-dating tools become ineffective. Our age distributions are compared to those derived from asteroseismic and giant samples and solar analogs. We are able to recover gyrochronological ages for old, lower-mainsequence stars, a remarkable improvement over prior work in hotter stars. Under our model assumptions, our ages have a median relative uncertainty of 14%, comparable to the age precision inferred for more massive stars using traditional methods. We investigate trends of galactic α-enhancement with age, finding evidence of a detection threshold between the age of the oldest α-poor stars and that of the bulk α-rich population. We argue that gyrochronology is an effective tool reaching ages of 10-12 Gyr in K-and early M-dwarfs. Finally, we present the first effort to quantify the impact of detailed abundance patterns on rotational evolution. We estimate a ∼ 15% bias in age for cool, α-enhanced (+ 0.4 dex) stars when standard solar-abundance-pattern rotational models are used for age inference, rather than models that appropriately account for α-enrichment. * Hubble Fellow tain abundances as proxies for age (e.g., Bensby et al. 2014; Martig et al. 2016; Tucci Maia et al. 2016; Feltzing et al. 2017). Other studies have argued against the thin-and thick-disk model of the Milky Way: as our ability to estimate precise stellar ages, composition, and kinematics has improved, the historical two-population hypothesis has evolved into a continuum of galactochemical structure and evolution (e.g., Bovy et al. 2012a,b; Buder et al. 2019). The study of chemical evolution in stellar populations is impossible without precise ages. To date, most investigations have used isochrones to estimate ages (Nordström et al. 2004; Haywood et al. 2013; Buder et al. 2019). While easy to implement, isochrone ages are most useful for cluster stars, which provide an ensemble of stars at a single age, or for field stars that have aged to about one-third of their main-sequence lifetimes (Pont & Eyer 2004; Soderblom 2010) and thus move substantially on the Hertzsprung-Russell (H-R) diagram. In this regime, isochrone ages are, at best, precise to 15%

Http Www Theses Fr, 2007

Cette these traite de l'etude de la dynamique de la zone radiative du Soleil. Le profil de ro... more Cette these traite de l'etude de la dynamique de la zone radiative du Soleil. Le profil de rotation dans la partie centrale du Soleil est encore mal connu alors que le coeur represente plus de 50% de la masse solaire. Pour une vision globale de l'evolution des etoiles, nous voulons mettre des contraintes sur les processus dynamiques ayant lieu dans le Soleil. Nous avons emprunte plusieurs voies pour cette etude: la modelisation, la mise au point et l'etude d'un nouvel instrument, les observations et les inversions de la rotation. Une meilleure comprehension de la dynamique solaire necessite la detection des modes de gravite. Pour cela, un prototype technologique construit au CEA (GOLF-NG) a pour but de valider des points techniques et de preparer une mission scientifique. Nous avons etudie le photodetecteur et l'instrument complet. Nous montrons sa faisabilite ainsi que son bon fonctionnement en observant la resonance des differents canaux. En attendant que cette mission prenne jour, l'analyse des donnees de GOLF, a bord de SoHO, nous a permis de detecter un candidat mode de gravite et d'observer la signature des modes de gravite dipolaires. Ce travail a en particulier beneficie d'une approche theorique sur les frequences de ces modes. Nous montrons l'impact de differents processus et quantites physiques sur ces predictions. Enfin, les processus dynamiques au sein du Soleil etant mal contraints, nous avons etudie l'impact de l'ajout d'un ou plusieurs modes de gravite dans les inversions sur les profils de rotation extraits. Enfin, nous donnons des contraintes sur les observations afin d'obtenir une information non negligeable sur le profil de rotation dans le cœur.

Nature, 2016

A knowledge of stellar ages is crucial for our understanding of many astrophysical phenomena, and... more A knowledge of stellar ages is crucial for our understanding of many astrophysical phenomena, and yet ages can be difficult to determine. As they become older, stars lose mass and angular momentum, resulting in an observed slowdown in surface rotation 1. The technique of 'gyrochronology' uses the rotation period of a star to calculate its age 2,3. However, stars of known age must be used for calibration, and, until recently, the approach was untested for old stars (older than 1 gigayear, Gyr). Rotation periods are now known for stars in an open cluster of intermediate age 4 (NGC 6819; 2.5 Gyr old), and for old field stars whose ages have been determined with asteroseismology 5,6. The data for the cluster agree with previous period-age relations 4 , but these relations fail to describe the asteroseismic sample 7. Here we report stellar evolutionary modelling 5, 6, 8, 9, 10 , and confirm the presence of unexpectedly rapid rotation in stars that are more evolved than the Sun. We demonstrate that models that incorporate dramatically weakened magnetic braking for old stars can-unlike existing models-reproduce both the asteroseismic and the cluster data. Our findings might suggest a fundamental change in the nature of ageing stellar dynamos, with the Sun being close to the critical transition to much weaker magnetized Stellar Astrophysics" program held from January to April 2015. We thank B. Shappee for useful discussion. T.S.M acknowledges the adopt-a-star crowdfunding program administered by White Dwarf Research Corp. G.R.D.

EPJ Web of Conferences, 2015

The knowledge of stellar ages directly impacts the characterization of a planetary system as it p... more The knowledge of stellar ages directly impacts the characterization of a planetary system as it puts strong constraints on the moment when the system was born. Unfortunately, the determination of precise stellar ages is a very difficult task. Different methods can be used to do so (based on isochrones or chemical element abundances) but they usually provide large uncertainties. During its evolution a star goes through processes leading to loss of angular momentum but also changes in its magnetic activity. Building rotation, magnetic, age relations would be an asset to infer stellar ages model independently. Several attempts to build empirical relations between rotation and age (namely gyrochronology) were made with a focus on cluster stars where the age determination is easier and for young stars on the main sequence. For field stars, we can now take advantage of high-precision photometric observations where we can perform asteroseismic analyses to improve the accuracy of stellar ages. Furthermore, the variability in the light curves allow us to put strong constraints on the stellar rotation and magnetic activity. By combining these precise measurements, we are on the way of understanding and improving relations between magnetic activity, rotation, and age, in particular at different stages of stellar evolution. I will review the status on gyrochronology relationships based on observations of young cluster stars. Then I will focus on solar-like stars and describe the inferences on stellar ages, rotation, and magnetism that can be provided by high-quality photometric observations such as the ones of the Kepler mission, in particular through asteroseismic analyses.

The Astrophysical Journal, 2014

The success of asteroseismology relies heavily on our ability to identify the frequency patterns ... more The success of asteroseismology relies heavily on our ability to identify the frequency patterns of stellar oscillation modes. For stars like the Sun this is relatively easy because the mode frequencies follow a regular pattern described by a well-founded asymptotic relation. When a solar like star evolves off the main sequence and onto the red giant branch its structure changes dramatically resulting in changes in the frequency pattern of the modes. We follow the evolution of the adiabatic frequency pattern from the main sequence to near the tip of the red giant branch for a series of models. We find a significant departure from the asymptotic relation for the non-radial modes near the red giant branch tip, resulting in a triplet frequency pattern. To support our investigation we analyze almost four years of Kepler data of the most luminous stars in the field (late K and early M type) and find that their frequency spectra indeed show a triplet pattern dominated by dipole modes even for the most luminous stars in our sample. Our identification explains previous results from ground-based observations reporting fine structure in the Petersen diagram and sub ridges in the period-luminosity diagram. Finally, we find 'new ridges' of non-radial modes with frequencies below the fundamental mode in our model calculations, and we speculate they are related to f modes.

Astronomy & Astrophysics, 2015

In asteroseismology, the observed time series often suffers from incomplete time coverage due to ... more In asteroseismology, the observed time series often suffers from incomplete time coverage due to gaps. The presence of periodic gaps may generate spurious peaks in the power spectrum that limit the analysis of the data. Various methods have been developed to deal with gaps in time series data. However, it is still important to improve these methods to be able to extract all the possible information contained in the data. In this paper, we propose a new approach to handling the problem, the so-called inpainting method. This technique, based on a prior condition of sparsity, enables the gaps in the data to be judiciously fill-in thereby preserving the asteroseismic signal as far as possible. The impact of the observational window function is reduced and the interpretation of the power spectrum simplified. This method is applied on both ground-and space-based data. It appears that the inpainting technique improves the detection and estimation of the oscillation modes. Additionally, it can be used to study very long time series of many stars because it is very fast to compute. For a time series of 50 days of CoRoT-like data, it allows a speed-up factor of 1000, if compared to methods with the same accuracy.

The Astrophysical Journal, 2014

Science, 2010

Observations of a distant star reveal a magnetic activity cycle similar to that of the Sun.

Arxiv preprint arXiv: …, 2011

The Astrophysical Journal, 2010

Recently, Karoff & Kjeldsen (2008) presented evidence of strong correlation between the energy in... more Recently, Karoff & Kjeldsen (2008) presented evidence of strong correlation between the energy in the high-frequency part (5.3<ν<8.3 mHz) of the acoustic spectrum of the Sun and the solar X-ray flux. They have used disk-integrated intensity observations of the Sun obtained from the VIRGO (Variability of solar IRradiance and Gravity Oscillations) instrument on board SOHO (Solar and Heliospheric Observatory) spacecraft. Similar signature of flares in velocity observations has not been confirmed till now. The study of low-degree high-frequency waves in the Sun is important for our understanding of the dynamics of the deeper solar layers. In this paper, we present the analysis of the velocity observations of the Sun obtained from the MDI (Michelson and Doppler Imager) and the GOLF (Global Oscillations at Low Frequencies) instruments on board SOHO for some major flare events of the solar cycle 23. Application of wavelet techniques to the time series of disk-integrated velocity signals from the solar surface using the full-disk Dopplergrams obtained from the MDI clearly indicates that there is enhancement of high-frequency global waves in the Sun during the flares. This signature of flares is also visible in the Fourier Power Spectrum of these velocity oscillations. On the other hand, the analysis of disk-integrated velocity observations obtained from the GOLF shows only marginal evidence of effects of flares on high-frequency oscillations.

Journal of Physics: Conference Series, 2013

We report the observations of a main-sequence star, HD 42618 (T eff = 5765 K, G3V) by the space t... more We report the observations of a main-sequence star, HD 42618 (T eff = 5765 K, G3V) by the space telescope CoRoT. This is the closest star to the Sun ever observed by CoRoT in term of its fundamental parameters. Using a preliminary version of CoRoT light curves of HD 42618, p modes are detected around 3.2 mHz associated to ℓ = 0, 1 and 2 modes with a large spacing of 142 µHz. Various methods are then used to derive the mass and radius of this star (scaling relations from solar values as well as comparison between theoretical and observationnal frequencies) giving values in the range of (0.80 − 1.02)M⊙ and (0.91 − 1.01)R⊙. A preliminary analysis of ℓ = 0 and 1 modes allows us also to study the amount of penetrative convection at the base of the convective envelope.

Journal of Physics: Conference Series, 2011

Journal of Physics: Conference Series, 2011

... Brajesh Kumar1, P. Venkatakrishnan1, Savita Mathur2, Sanjiv Kumar Tiwari1 and RA Garcıa3 1 Ud... more ... Brajesh Kumar1, P. Venkatakrishnan1, Savita Mathur2, Sanjiv Kumar Tiwari1 and RA Garcıa3 1 Udaipur Solar Observatory, Physical Research Laboratory, Dewali, Badi Road, Udaipur 313004, INDIA 2 High Altitude ... Journal of Physics: Conference Series 271 (2011) 012020 ...

HAL (Le Centre pour la Communication Scientifique Directe), Oct 1, 2011

More than 1000 red giants have been observed by NASA/Kepler mission during a nearly continuous pe... more More than 1000 red giants have been observed by NASA/Kepler mission during a nearly continuous period of ∼ 13 months. The resulting high-frequency resolution (< 0.03 µHz) allows us to study the granulation parameters of these stars. The granulation pattern results from the convection motions leading to upward flows of hot plasma and downward flows of cooler plasma. We fitted Harvey-like functions to the power spectra, to retrieve the timescale and amplitude of granulation. We show that there is an anti-correlation between both of these parameters and the position of maximum power of acoustic modes, while we also find a correlation with the radius, which agrees with the theory. We finally compare our results with 3D models of the convection.

The Astronomical Journal, 2020

A-970. Based on observations obtained with the Nordic Optical Telescope (NOT), operated on the is... more A-970. Based on observations obtained with the Nordic Optical Telescope (NOT), operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos (ORM) of the Instituto de Astrofísica de Canarias (IAC). This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. This work makes use of observations from the LCOGT network.

The Astrophysical Journal, 2020

We use models of stellar angular momentum evolution to determine ages for ∼ 500 stars in the APOG... more We use models of stellar angular momentum evolution to determine ages for ∼ 500 stars in the APOGEE-Kepler Cool Dwarfs sample. We focus on lower main-sequence stars, where other age-dating tools become ineffective. Our age distributions are compared to those derived from asteroseismic and giant samples and solar analogs. We are able to recover gyrochronological ages for old, lower-mainsequence stars, a remarkable improvement over prior work in hotter stars. Under our model assumptions, our ages have a median relative uncertainty of 14%, comparable to the age precision inferred for more massive stars using traditional methods. We investigate trends of galactic α-enhancement with age, finding evidence of a detection threshold between the age of the oldest α-poor stars and that of the bulk α-rich population. We argue that gyrochronology is an effective tool reaching ages of 10-12 Gyr in K-and early M-dwarfs. Finally, we present the first effort to quantify the impact of detailed abundance patterns on rotational evolution. We estimate a ∼ 15% bias in age for cool, α-enhanced (+ 0.4 dex) stars when standard solar-abundance-pattern rotational models are used for age inference, rather than models that appropriately account for α-enrichment. * Hubble Fellow tain abundances as proxies for age (e.g., Bensby et al. 2014; Martig et al. 2016; Tucci Maia et al. 2016; Feltzing et al. 2017). Other studies have argued against the thin-and thick-disk model of the Milky Way: as our ability to estimate precise stellar ages, composition, and kinematics has improved, the historical two-population hypothesis has evolved into a continuum of galactochemical structure and evolution (e.g., Bovy et al. 2012a,b; Buder et al. 2019). The study of chemical evolution in stellar populations is impossible without precise ages. To date, most investigations have used isochrones to estimate ages (Nordström et al. 2004; Haywood et al. 2013; Buder et al. 2019). While easy to implement, isochrone ages are most useful for cluster stars, which provide an ensemble of stars at a single age, or for field stars that have aged to about one-third of their main-sequence lifetimes (Pont & Eyer 2004; Soderblom 2010) and thus move substantially on the Hertzsprung-Russell (H-R) diagram. In this regime, isochrone ages are, at best, precise to 15%

Http Www Theses Fr, 2007

Cette these traite de l'etude de la dynamique de la zone radiative du Soleil. Le profil de ro... more Cette these traite de l'etude de la dynamique de la zone radiative du Soleil. Le profil de rotation dans la partie centrale du Soleil est encore mal connu alors que le coeur represente plus de 50% de la masse solaire. Pour une vision globale de l'evolution des etoiles, nous voulons mettre des contraintes sur les processus dynamiques ayant lieu dans le Soleil. Nous avons emprunte plusieurs voies pour cette etude: la modelisation, la mise au point et l'etude d'un nouvel instrument, les observations et les inversions de la rotation. Une meilleure comprehension de la dynamique solaire necessite la detection des modes de gravite. Pour cela, un prototype technologique construit au CEA (GOLF-NG) a pour but de valider des points techniques et de preparer une mission scientifique. Nous avons etudie le photodetecteur et l'instrument complet. Nous montrons sa faisabilite ainsi que son bon fonctionnement en observant la resonance des differents canaux. En attendant que cette mission prenne jour, l'analyse des donnees de GOLF, a bord de SoHO, nous a permis de detecter un candidat mode de gravite et d'observer la signature des modes de gravite dipolaires. Ce travail a en particulier beneficie d'une approche theorique sur les frequences de ces modes. Nous montrons l'impact de differents processus et quantites physiques sur ces predictions. Enfin, les processus dynamiques au sein du Soleil etant mal contraints, nous avons etudie l'impact de l'ajout d'un ou plusieurs modes de gravite dans les inversions sur les profils de rotation extraits. Enfin, nous donnons des contraintes sur les observations afin d'obtenir une information non negligeable sur le profil de rotation dans le cœur.

Nature, 2016

A knowledge of stellar ages is crucial for our understanding of many astrophysical phenomena, and... more A knowledge of stellar ages is crucial for our understanding of many astrophysical phenomena, and yet ages can be difficult to determine. As they become older, stars lose mass and angular momentum, resulting in an observed slowdown in surface rotation 1. The technique of 'gyrochronology' uses the rotation period of a star to calculate its age 2,3. However, stars of known age must be used for calibration, and, until recently, the approach was untested for old stars (older than 1 gigayear, Gyr). Rotation periods are now known for stars in an open cluster of intermediate age 4 (NGC 6819; 2.5 Gyr old), and for old field stars whose ages have been determined with asteroseismology 5,6. The data for the cluster agree with previous period-age relations 4 , but these relations fail to describe the asteroseismic sample 7. Here we report stellar evolutionary modelling 5, 6, 8, 9, 10 , and confirm the presence of unexpectedly rapid rotation in stars that are more evolved than the Sun. We demonstrate that models that incorporate dramatically weakened magnetic braking for old stars can-unlike existing models-reproduce both the asteroseismic and the cluster data. Our findings might suggest a fundamental change in the nature of ageing stellar dynamos, with the Sun being close to the critical transition to much weaker magnetized Stellar Astrophysics" program held from January to April 2015. We thank B. Shappee for useful discussion. T.S.M acknowledges the adopt-a-star crowdfunding program administered by White Dwarf Research Corp. G.R.D.

EPJ Web of Conferences, 2015

The knowledge of stellar ages directly impacts the characterization of a planetary system as it p... more The knowledge of stellar ages directly impacts the characterization of a planetary system as it puts strong constraints on the moment when the system was born. Unfortunately, the determination of precise stellar ages is a very difficult task. Different methods can be used to do so (based on isochrones or chemical element abundances) but they usually provide large uncertainties. During its evolution a star goes through processes leading to loss of angular momentum but also changes in its magnetic activity. Building rotation, magnetic, age relations would be an asset to infer stellar ages model independently. Several attempts to build empirical relations between rotation and age (namely gyrochronology) were made with a focus on cluster stars where the age determination is easier and for young stars on the main sequence. For field stars, we can now take advantage of high-precision photometric observations where we can perform asteroseismic analyses to improve the accuracy of stellar ages. Furthermore, the variability in the light curves allow us to put strong constraints on the stellar rotation and magnetic activity. By combining these precise measurements, we are on the way of understanding and improving relations between magnetic activity, rotation, and age, in particular at different stages of stellar evolution. I will review the status on gyrochronology relationships based on observations of young cluster stars. Then I will focus on solar-like stars and describe the inferences on stellar ages, rotation, and magnetism that can be provided by high-quality photometric observations such as the ones of the Kepler mission, in particular through asteroseismic analyses.

The Astrophysical Journal, 2014

The success of asteroseismology relies heavily on our ability to identify the frequency patterns ... more The success of asteroseismology relies heavily on our ability to identify the frequency patterns of stellar oscillation modes. For stars like the Sun this is relatively easy because the mode frequencies follow a regular pattern described by a well-founded asymptotic relation. When a solar like star evolves off the main sequence and onto the red giant branch its structure changes dramatically resulting in changes in the frequency pattern of the modes. We follow the evolution of the adiabatic frequency pattern from the main sequence to near the tip of the red giant branch for a series of models. We find a significant departure from the asymptotic relation for the non-radial modes near the red giant branch tip, resulting in a triplet frequency pattern. To support our investigation we analyze almost four years of Kepler data of the most luminous stars in the field (late K and early M type) and find that their frequency spectra indeed show a triplet pattern dominated by dipole modes even for the most luminous stars in our sample. Our identification explains previous results from ground-based observations reporting fine structure in the Petersen diagram and sub ridges in the period-luminosity diagram. Finally, we find 'new ridges' of non-radial modes with frequencies below the fundamental mode in our model calculations, and we speculate they are related to f modes.

Astronomy & Astrophysics, 2015

In asteroseismology, the observed time series often suffers from incomplete time coverage due to ... more In asteroseismology, the observed time series often suffers from incomplete time coverage due to gaps. The presence of periodic gaps may generate spurious peaks in the power spectrum that limit the analysis of the data. Various methods have been developed to deal with gaps in time series data. However, it is still important to improve these methods to be able to extract all the possible information contained in the data. In this paper, we propose a new approach to handling the problem, the so-called inpainting method. This technique, based on a prior condition of sparsity, enables the gaps in the data to be judiciously fill-in thereby preserving the asteroseismic signal as far as possible. The impact of the observational window function is reduced and the interpretation of the power spectrum simplified. This method is applied on both ground-and space-based data. It appears that the inpainting technique improves the detection and estimation of the oscillation modes. Additionally, it can be used to study very long time series of many stars because it is very fast to compute. For a time series of 50 days of CoRoT-like data, it allows a speed-up factor of 1000, if compared to methods with the same accuracy.

The Astrophysical Journal, 2014

Science, 2010

Observations of a distant star reveal a magnetic activity cycle similar to that of the Sun.

Arxiv preprint arXiv: …, 2011

The Astrophysical Journal, 2010

Recently, Karoff & Kjeldsen (2008) presented evidence of strong correlation between the energy in... more Recently, Karoff & Kjeldsen (2008) presented evidence of strong correlation between the energy in the high-frequency part (5.3<ν<8.3 mHz) of the acoustic spectrum of the Sun and the solar X-ray flux. They have used disk-integrated intensity observations of the Sun obtained from the VIRGO (Variability of solar IRradiance and Gravity Oscillations) instrument on board SOHO (Solar and Heliospheric Observatory) spacecraft. Similar signature of flares in velocity observations has not been confirmed till now. The study of low-degree high-frequency waves in the Sun is important for our understanding of the dynamics of the deeper solar layers. In this paper, we present the analysis of the velocity observations of the Sun obtained from the MDI (Michelson and Doppler Imager) and the GOLF (Global Oscillations at Low Frequencies) instruments on board SOHO for some major flare events of the solar cycle 23. Application of wavelet techniques to the time series of disk-integrated velocity signals from the solar surface using the full-disk Dopplergrams obtained from the MDI clearly indicates that there is enhancement of high-frequency global waves in the Sun during the flares. This signature of flares is also visible in the Fourier Power Spectrum of these velocity oscillations. On the other hand, the analysis of disk-integrated velocity observations obtained from the GOLF shows only marginal evidence of effects of flares on high-frequency oscillations.

Journal of Physics: Conference Series, 2013

We report the observations of a main-sequence star, HD 42618 (T eff = 5765 K, G3V) by the space t... more We report the observations of a main-sequence star, HD 42618 (T eff = 5765 K, G3V) by the space telescope CoRoT. This is the closest star to the Sun ever observed by CoRoT in term of its fundamental parameters. Using a preliminary version of CoRoT light curves of HD 42618, p modes are detected around 3.2 mHz associated to ℓ = 0, 1 and 2 modes with a large spacing of 142 µHz. Various methods are then used to derive the mass and radius of this star (scaling relations from solar values as well as comparison between theoretical and observationnal frequencies) giving values in the range of (0.80 − 1.02)M⊙ and (0.91 − 1.01)R⊙. A preliminary analysis of ℓ = 0 and 1 modes allows us also to study the amount of penetrative convection at the base of the convective envelope.

Journal of Physics: Conference Series, 2011

Journal of Physics: Conference Series, 2011

... Brajesh Kumar1, P. Venkatakrishnan1, Savita Mathur2, Sanjiv Kumar Tiwari1 and RA Garcıa3 1 Ud... more ... Brajesh Kumar1, P. Venkatakrishnan1, Savita Mathur2, Sanjiv Kumar Tiwari1 and RA Garcıa3 1 Udaipur Solar Observatory, Physical Research Laboratory, Dewali, Badi Road, Udaipur 313004, INDIA 2 High Altitude ... Journal of Physics: Conference Series 271 (2011) 012020 ...