Stellar Luminosity Research Articles

Annual parallax measurement of the Mira variable star BX Camelopardalis with VERA

Abstract We report the results of astrometric VLBI observations toward the Mira variable star BX Cam using the VERA VLBI array. The observation was performed from 2012 February to 2014 November. The parallax obtained is 1.73 ± 0.03 mas corresponding to a distance of 0.58 ± 0.01 kpc. The parallax of this source was reported in Gaia DR2 as 4.13 ± 0.25 mas, and there is a 240% difference between these two measurements. Astrometric results from our VLBI observations show that we exactly traced the angular motions of the seven maser spots in BX Cam. We calculated the stellar luminosities using both parallaxes, and obtained luminosities of $L_{\ast }^{\mathrm{VERA}} = 4950\pm 170\, L_{\odot }$ and $L_{\ast }^{\mathrm{Gaia}} = 870\pm 110\, L_{\odot }$. These deduced luminosities also support the validity of the parallax that we determined with VERA. Evaluating the two parallaxes, we conclude that the parallax of 1.73 ± 0.03 mas from the VERA observations is correct for BX Cam. We obtained the systemic motion of BX Cam as (μαcos δsys, ${\mu }_{\delta }^{\mathrm{sys}}$) = (13.48 ± 0.14, −34.30 ± 0.18) mas yr−1. The total of 73 H2O maser spots detected from our VLBI observations shows a spatial distribution of 30 au × 80 au, with a strong elongation along the north–south direction. They show outflows with a three-dimensional velocity of 14.79 ± 1.40 km s−1. From a comparison between the time variations of the V-band magnitudes and the H2O masers, we found that the variation of the H2O masers is relevant to that seen in the V band even though the H2O masers do not recover their maximum flux in each cycle.

When more is less: The P‐type binary habitability paradox

AbstractIn the case of single stars, larger stellar luminosities always entail larger habitable zones (HZs). If the stellar luminosity is increased, the HZs are established at larger stellar distances, and their widths are broader. However, studies have shown that this behavior is not necessarily the case for P‐type HZs of binary systems. In some of those systems, the width of the circumbinary HZ is smaller (or even nonexisting) than the width of the primary's HZ if they are considered a single star—an obvious paradox considering that the total luminosity of the binary is always larger than that of the system's primary. Here, we present a tutorial study of this behavior for theoretical main‐sequence stars with the combined masses of the stellar components equal to two solar masses. The planetary climate models are chosen in correspondence to the general HZ. The paradox is found to occur for systems of relatively unequal stellar masses (or luminosities) or in systems where the separation distances or eccentricities of the stellar components are relatively large.

Massive discs around low-mass stars

ABSTRACT We use a suite of smoothed particle hydrodynamic simulations to investigate the susceptibility of protoplanetary discs to the effects of self-gravity as a function of star–disc properties. We also include passive irradiation from the host star using different models for the stellar luminosities. The critical disc-to-star mass ratio for axisymmetry (for which we produce criteria) increases significantly for low-mass stars. This could have important consequences for increasing the potential mass reservoir in a proto Trappist-1 system, since even the efficient Ormel et al. formation model will be influenced by processes like external photoevaporation, which can rapidly and dramatically deplete the dust reservoir. The aforementioned scaling of the critical Md/M* for axisymmetry occurs in part because the Toomre Q parameter has a linear dependence on surface density (which promotes instability) and only an $M_*^{1/2}$ dependence on shear (which reduces instability), but also occurs because, for a given Md/M*, the thermal evolution depends on the host star mass. The early phase stellar irradiation of the disc (for which the luminosity is much higher than at the zero age main sequence, particularly at low stellar masses) can also play a key role in significantly reducing the role of self-gravity, meaning that even solar mass stars could support axisymmetric discs a factor two higher in mass than usually considered possible. We apply our criteria to the DSHARP discs with spirals, finding that self-gravity can explain the observed spirals so long as the discs are optically thick to the host star irradiation.

Determining the size of the helium core of KIC 9970396 using asteroseismology: a red giant approaching the red giant bump

ABSTRACT Mixed modes are less affected by the surface effect and carry internal information of a star. Asteroseismic modelling of mixed modes can constrain the size of the helium core of a star. Previous work has shown that the evolution stage of KIC 9970396 may be near the red giant bump phase, which is one of the most interesting regions in the red giant evolution stage. It is known that there is a clear relation between the core and mass luminosity, following homological principles on the low-luminosity giant branch. Our aim in this paper is to determine the size of the helium core and constrain the internal structure of the star. Our approach is first to identify the most p-dominated frequencies in the observational mixed modes. The calculated frequencies are then fitted to the observational frequencies, which we choose not to correct for surface effect offsets. We have computed a grid of theoretical models to fit the l = 1 modes of KIC 9970396. The size of the helium core of KIC 9970396 is determined to be MHe = 0.229 ± 0.001 M⊙ and RHe = 0.03055 ± 0.00015 R⊙. The best-fitting model shows that KIC 9970396 is undergoing a stage that is between the first dredge-up event and the red giant bump. Compared with the results of our model, the previous core–mass luminosity relation overestimates the helium core mass by 0.009 M⊙ when the stellar luminosity of a red giant star is known.

Subaru Infrared Adaptive Optics-assisted High-spatial-resolution Imaging Search for Luminous Dual Active Galactic Nuclei in Nearby Ultraluminous Infrared Galaxies

Abstract We present infrared K′-band (2.1 μm) and L′-band (3.8 μm) high-spatial-resolution (<0.″3) imaging observations of 17 nearby (z < 0.17) ultraluminous infrared galaxies (ULIRGs) assisted with the adaptive optics of the Subaru Telescope. We search for compact red K′ − L′ color emission as the indicator of luminous active galactic nuclei (AGNs) due to AGN-heated hot dust emission. Two luminous dual AGN candidates are revealed. Combining these results with those of our previous study, we can state that the detected fraction of luminous dual AGNs in nearby ULIRGs is much less than unity (<20%), even when infrared wavelengths >2 μm are used that should be sensitive to buried AGNs due to small dust extinction effects. For ULIRGs with resolved multiple nuclear K′-band emission, we estimate the activation of supermassive black holes (SMBHs) in individual galaxy nuclei in the form of AGN luminosity normalized by SMBH mass inferred from the stellar luminosity of the host galaxy. We confirm a trend that more massive SMBHs in K′-band brighter primary galaxy nuclei are generally more active, with higher SMBH-mass-normalized AGN luminosity, than less massive SMBHs in K′-band fainter secondary galaxy nuclei, as predicted by numerical simulations of gas-rich major galaxy mergers. In two sources, the presence of even infrared-elusive extremely deeply buried AGNs is indicated by comparisons with available (sub)millimeter data. Non-synchronous SMBH activation (i.e., less activation of less massive SMBHs) and the possible presence of such infrared-elusive AGNs may be responsible for the small fraction of infrared-detected luminous dual AGNs in nearby merging ULIRGs.

Integrated Characteristics of SDSS DR14 Star-Forming Galaxies with Extremely Low Oxygen Abundances

Integrated characteristics of a sample of 66 star-forming galaxies with extremely low oxygen abundances from the SDSS Data Release 14 are studied. The oxygen abundances were determined by the direct Te method for 42 galaxies with detected [O III] 436.3 nm emission lines and by the strong-line method for the remaining galaxies. Derived abundances 12 + log (O/H) fall within the 6.97–7.52 range and are, on average, four times lower than the corresponding values for a large comparison sample of compact star-forming galaxies from the SDSS. Stellar masses and Hβ luminosities for both samples were derived from SDSS spectra with a small spectroscopic aperture (2–3 arcsec in diameter). In order to determine their values for the entire galaxy, aperture corrections taking radiation outside the spectroscopic slit into account were introduced. Stellar masses and luminosities in the optical range are 100 times lower than the corresponding values for the galaxies from the comparison sample. At fixed values of luminosity and stellar mass, these galaxies have lower oxygen abundances in the oxygen abundance–luminosity and oxygen abundance–stellar mass diagrams than the galaxies from the main SDSS sample. This offset is likely caused by accretion of unenriched intergalactic gas, which reduces the oxygen abundance in the galactic interstellar medium. The majority of galaxies with extremely low oxygen abundances were detected in the mid-infrared range by the WISE space telescope. Color index W1 – W2, where W1 and W2 are the magnitudes at a wavelength of 3.4 and 4.6 μm, of these galaxies corresponds to the values typical for stellar emission and/or free-free ionized gas emission. The low ultraviolet luminosity, which is the main source of dust heating in star-forming galaxies, thus eliminates the possibility that warm and hot dust is present.

The Stars in M15 Were Born with the r-process*

Abstract High-resolution spectroscopy of stars on the red giant branch (RGB) of the globular cluster M15 has revealed a large (∼1 dex) dispersion in the abundances of r-process elements such as Ba and Eu. Neutron star mergers (NSMs) have been proposed as a major source of the r-process. However, most NSM models predict a delay time longer than the timescale for cluster formation. One possibility is that a NSM polluted the surfaces of stars in M15 long after the cluster finished forming. In this case, the abundances of the polluting elements would decrease in the first dredge-up as stars turn on to the RGB. We present Keck/DEIMOS abundances of Ba in 66 stars along the entire RGB and the top of the main sequence. The Ba abundances have no trend with stellar luminosity (evolutionary phase). Therefore, the stars were born with the Ba that they have today, and Ba did not originate in a source with a delay time longer than the timescale for cluster formation. In particular, if the source of Ba was a NSM, it would have had a very short delay time. Alternatively, if Ba enrichment took place before the formation of the cluster, an inhomogeneity of a factor of 30 in Ba abundance needs to be able to persist over the length scale of the gas cloud that formed M15, which is unlikely.

Stellar wind models of central stars of planetary nebulae

Context. Fast line-driven stellar winds play an important role in the evolution of planetary nebulae, even though they are relatively weak. Aims. We provide global (unified) hot star wind models of central stars of planetary nebulae. The models predict wind structure including the mass-loss rates, terminal velocities, and emergent fluxes from basic stellar parameters. Methods. We applied our wind code for parameters corresponding to evolutionary stages between the asymptotic giant branch and white dwarf phases for a star with a final mass of 0.569 M⊙. We study the influence of metallicity and wind inhomogeneities (clumping) on the wind properties. Results. Line-driven winds appear very early after the star leaves the asymptotic giant branch (at the latest for Teff ≈ 10 kK) and fade away at the white dwarf cooling track (below Teff = 105 kK). Their mass-loss rate mostly scales with the stellar luminosity and, consequently, the mass-loss rate only varies slightly during the transition from the red to the blue part of the Hertzsprung–Russell diagram. There are the following two exceptions to the monotonic behavior: a bistability jump at around 20 kK, where the mass-loss rate decreases by a factor of a few (during evolution) due to a change in iron ionization, and an additional maximum at about Teff = 40−50 kK. On the other hand, the terminal velocity increases from about a few hundreds of km s−1 to a few thousands of km s−1 during the transition as a result of stellar radius decrease. The wind terminal velocity also significantly increases at the bistability jump. Derived wind parameters reasonably agree with observations. The effect of clumping is stronger at the hot side of the bistability jump than at the cool side. Conclusions. Derived fits to wind parameters can be used in evolutionary models and in studies of planetary nebula formation. A predicted bistability jump in mass-loss rates can cause the appearance of an additional shell of planetary nebula.

Planet gap opening across stellar masses

ABSTRACT Annular structures in protoplanetary discs, such as gaps and rings, are now ubiquitously found by high-resolution Atacama Large Millimetre Array observations. Under the hypothesis that they are opened by planets, in this paper we investigate how the minimum planet mass needed to open a gap varies across different stellar host masses and distances from the star. The dependence on the stellar host mass is particularly interesting because, at least in principle, gap opening around low-mass stars should be possible for lower mass planets, giving us a look into the young, low-mass planet population. Using dusty hydrodynamical simulations, we find however the opposite behaviour, as a result of the fact that discs around low-mass stars are geometrically thicker: gap opening around low-mass stars can require more massive planets. Depending on the theoretical isochrone employed to predict the relationship between stellar mass and luminosity, the gap opening planet mass could also be independent of stellar mass, but in no case we find that gap opening becomes easier around low-mass stars. This would lead to the expectation of a lower incidence of such structures in lower mass stars, since exoplanet surveys show that low-mass stars have a lower fraction of giant planets. More generally, our study enables future imaging observations as a function of stellar mass to be interpreted using information on the mass versus luminosity relations of the observed samples.

A Simple Unified Spectroscopic Indicator of Stellar Luminosity: The Extended Flux-weighted Gravity–Luminosity Relationship

Abstract We show that for a wide range of stellar masses, from 0.3 to 20 M ⊙, and for evolutionary phases from the main sequence to the beginning of the red giant stage, the stellar flux-weighted gravity, g F ≡ g/ , is tightly correlated with absolute bolometric magnitude . Such a correlation is predicted by stellar evolution theory. We confirm this relation observationally, using a sample of 445 stars with precise stellar parameters. It holds over 17 stellar magnitudes from = 9.0 to −8.0 mag with a scatter of 0.17 mag above = −3.0 and 0.29 mag below this value. We then test the relation with 2.2 million stars with 6.5 mag ≥ ≥ 0.5 mag, where “mass-produced” but robust , and from LAMOST DR5 and Gaia DR2 are available. We find that the same relation holds with a scatter of ∼0.2 mag for single stars offering a simple spectroscopic distance estimate good to ∼10%.

Candidate LBV stars in galaxy NGC 7793 found via HST photometry + MUSE spectroscopy

ABSTRACT Only about 19 Galactic and 25 extragalactic bonafide luminous blue variables (LBVs) are known to date. This incomplete census prevents our understanding of this crucial phase of massive star evolution which leads to the formation of heavy binary black holes via the classical channel. With large samples of LBVs one could better determine the duration and maximum stellar luminosity which characterize this phase. We search for candidate LBVs (cLBVs) in a new galaxy, NGC 7793. For this purpose, we combine high spatial resolution images from two Hubble Space Telescope (HST) programs with optical spectroscopy from the Multi Unit Spectroscopic Explorer (MUSE). By combining PSF-fitting photometry measured on F547M, F657N, and F814W images, with restrictions on point-like appearance (at HST resolution) and H α luminosity, we find 100 potential cLBVs, 36 of which fall in the MUSE fields. Five of the latter 36 sources are promising cLBVs which have MV ≤ −7 and a combination of: H α with a P-Cygni profile; no [O i]$\, \lambda 6300$ emission; weak or no [O iii]$\, \lambda 5007$ emission; large [N ii]/H α relative to H ii regions; and [S ii]$\, \lambda 6716$/[S ii]$\, \lambda 6731\sim 1$. It is not clear if these five cLBVs are isolated from O-type stars, which would favour the binary formation scenario of LBVs. Our study, which approximately covers one fourth of the optical disc of NGC 7793, demonstrates how by combining the above HST surveys with multi-object spectroscopy from 8-m class telescopes, one can efficiently find large samples of cLBVs in nearby galaxies.

Long-term multi-frequency maser observations of the intermediate-mass young stellar object G107.298+5.639

Context. Periodic flares of maser emission are thought to be induced either by variations of the seed photon flux in young binary systems or the pump rate regulated by stellar and accretion luminosities. Aims. We seek to study the variability of four maser transitions of three different species in G107.298+5.639 to constrain the dominant mechanism of periodic flares. Methods. Light curves of the 6.7 GHz methanol and 22.2 GHz water vapour maser were obtained with the Torun 32 m radio telescope over 39 and 34 cycles, respectively. The target was also monitored at the 1.6 GHz hydroxyl transitions with the Nançay radio telescope over 13 cycles. All these maser lines were imaged using VLBI arrays. Results. The study confirms alternating flares of the methanol and water masers with a period of 34.4 d and reveals the synchronised behaviour of the methanol and hydroxyl masers in this source. The observed spatial distribution of the methanol maser cloudlets and the measured time delays of the flares of individual features imply a ring-like structure of radius 240 au and thickness 30 au. Internal proper motions indicate that the velocity of methanol cloudlets is dominated by a disc-wind component of about 5 km s−1. The methanol emission detected during only one VLBI observation is located in a region about 550 au from a central star, which also exhibits OH maser flares. The erratic appearance of methanol features can be related to a powering object of relatively low luminosity which, during some variability cycles, can excite molecules only in the nearest part of the disc. A careful analysis of the maser and infrared light curves reveal a strong correlation between the 6.7 GHz line and the infrared flux densities supporting a radiative pumping of the maser. Conclusions. The synchronised behaviour of the hydroxyl 1665/1667 MHz and 6.7 GHz methanol transitions indicates a common pumping mechanism for the periodic flares of G107.298+5.639.

Eating Planets for Lunch and Dinner: Signatures of Planet Consumption by Evolving Stars

Abstract Exoplanets have been observed around stars at all stages of stellar evolution, in many cases orbiting in configurations that will eventually lead to the planets being engulfed or consumed by their host stars, such as hot Jupiters or ultrashort period planets. Furthermore, objects such as polluted white dwarfs provide strong evidence that the consumption of planets by stars is a common phenomenon. This consumption causes several significant changes in the stellar properties, such as changes to the stellar spin, luminosity, chemical composition, or mass-loss processes. Here, we explore this wide variety of effects for a comprehensive range of stellar and planetary masses and stages of stellar evolution, from the main sequence over red giants to white dwarfs. We determine that planet consumption can cause transient luminosity features that last on the order of centuries to millennia, and that the post-consumption stellar spins can often reach breakup speeds. Furthermore, stellar mass loss can be caused by this spin-up, as well as through surface grazing interactions, leading to to the formation of unusual planetary nebula shapes or collimated stellar gas ejections. Our results highlight several observable stellar features by which the presence or previous existence of a planet around a given star can be deduced. This will provide future observational campaigns with the tools to better constrain exoplanet demographics, as well as planetary formation and evolution histories.

Temperature of Interstellar Space Revisited by Relational Approach

The article features an interpretation of the cosmic microwave background (CMB) radiation in the framework of the relational approach. The key concept of the proposed interpretation is strongly connected with the ideas on the ‘‘temperature of interstellar space’’ put forward by Weyl, Eddington, Regener and Nernst in the 1920s–1930s. In accordance with the relational justification of the cosmological redshift and modern data on stellar luminosities, a new estimate of the CMB temperature is obtained.

The Mass Relations between Supermassive Black Holes and Their Host Galaxies at 1 < z < 2 with HST-WFC3

Abstract Correlations between the mass of a supermassive black hole (SMBH) and the properties of its host galaxy (e.g., total stellar mass M *, luminosity L host) suggest an evolutionary connection. A powerful test of a coevolution scenario is to measure the relations  BH –L host and  BH –M * at high redshift and compare with local estimates. For this purpose, we acquired Hubble Space Telescope (HST) imaging with WFC3 of 32 X-ray-selected broad-line (type 1) active galactic nuclei at 1.2 < z < 1.7 in deep survey fields. By applying state-of-the-art tools to decompose the HST images including available ACS data, we measured the host galaxy luminosity and stellar mass along with other properties through the two-dimensional model fitting. The black hole mass (  BH ) was determined using the broad Hα line, detected in the near-infrared with the Subaru Fiber Multi-Object Spectrograph, which potentially minimizes systematic effects using other indicators. We find that the observed ratio of  BH to total M * is 2.7× larger at z ∼ 1.5 than in the local universe, while the scatter is equivalent between the two epochs. A nonevolving mass ratio is consistent with the data at the 2σ–3σ confidence level when accounting for selection effects (estimated using two independent and complementary methods) and their uncertainties. The relationship between  BH and host galaxy total luminosity paints a similar picture. Therefore, our results cannot distinguish whether SMBHs and their total host stellar mass and luminosity proceed in lockstep or whether the growth of the former somewhat overshoots the latter, given the uncertainties. Based on a statistical estimate of the bulge-to-total mass fraction, the ratio  BH /M *,bulge is offset from the local value by a factor of ∼7, which is significant even accounting for selection effects. Taken together, these observations are consistent with a scenario in which stellar mass is subsequently transferred from an angular momentum–supported component of the galaxy to a pressure-supported one through secular processes or minor mergers at a faster rate than mass accretion onto the SMBH.

Neutrino luminosity of stars with different masses

Neutrinos play an important role in stellar evolution. They are produced by nuclear reactions or thermal processes. Using the stellar evolution code Modules for Experiments in Stellar Astrophysics (MESA), we study stellar neutrino luminosity with different masses. The neutrino luminosities of stars with different initial masses at different evolutionary stages are simulated. We find that the neutrino flux of a star with 1 M⊙ mass at an evolutionary age of 4.61 × 109 yr is consistent with that of the Sun. In general, neutrinos are produced by nuclear reactions, and the neutrino luminosity of stars is about one or two magnitudes lower than the photo luminosity. However, neutrino luminosity can exceed photo luminosity during the helium flash which can occur for stars with a mass lower than 8 M⊙. Although the helium flash does not produce neutrinos, plasma decay, one of the thermal processes, can efficiently make neutrinos during this stage. Due to the high mass-loss rate, a star with a mass of 9 M⊙ does not undergo the helium flash. Its neutrinos mainly originate from nuclear reactions until the end of the AGB stage. At the end of the AGB stage, its neutrino luminosity results from plasma decay which is triggered by the gravitational energy release because of the stellar core contracting.

The ALMA Frontier Fields Survey

Context. The Hubble Frontier Fields offer an exceptionally deep window into the high-redshift universe, covering a substantially larger area than the Hubble Ultra-Deep field at low magnification and probing 1–2 mag deeper in exceptional high-magnification regions. This unique parameter space, coupled with the exceptional multi-wavelength ancillary data, can facilitate for useful insights into distant galaxy populations. Aims. We aim to leverage Atacama Large Millimetre Array (ALMA) band 6 (≈263 GHz) mosaics in the central portions of five Frontier Fields to characterize the infrared (IR) properties of 1582 ultraviolet (UV)-selected Lyman-Break Galaxies (LBGs) at redshifts of z ∼ 2–8. We investigated individual and stacked fluxes and IR excess (IRX) values of the LBG sample as functions of stellar mass (M⋆), redshift, UV luminosity and slope β, and lensing magnification. Methods. LBG samples were derived from color-selection and photometric redshift estimation with Hubble Space Telescope photometry. Spectral energy distributions -templates were fit to obtain luminosities, stellar masses, and star formation rates for the LBG candidates. We obtained individual IR flux and IRX estimates, as well as stacked averages, using both ALMA images and u–v visibilities. Results. Two (2) LBG candidates were individually detected above a significance of 4.1-σ, while stacked samples of the remaining LBG candidates yielded no significant detections. We investigated our detections and upper limits in the context of the IRX–M⋆ and IRX–β relations, probing at least one dex lower in stellar mass than past studies have done. Our upper limits exclude substantial portions of parameter space and they are sufficiently deep in a handful of cases to create mild tension with the typically assumed attenuation and consensus relations. We observe a clear and smooth trend between M⋆ and β, which extends to low masses and blue (low) β values, consistent with expectations from previous works.

Post-main-sequence debris from rotation-induced YORP break-up of small bodies – II. Multiple fissions, internal strengths, and binary production

ABSTRACT Over one-quarter of white dwarfs contain observable metallic debris from the break-up of exo-asteroids. Understanding the physical and orbital history of this debris would enable us to self-consistently link planetary system formation and fate. One major debris reservoir is generated by YORP-induced rotational fission during the giant branch phases of stellar evolution, where the stellar luminosity can exceed the Sun’s by four orders of magnitude. Here, we determine the efficacy of the giant branch YORP effect for asteroids with non-zero internal strength, and model post-fission evolution by imposing simple analytic fragmentation prescriptions. We find that even the highest realistic internal strengths cannot prevent the widespread fragmentation of asteroids and the production of a debris field over 100 au in size. We compute the number of successive fission events as they occur in progressively smaller time intervals as the star ascends the giant branches, providing a way to generate size distributions of asteroid fragments. The results are highly insensitive to progenitor stellar mass. We also conclude that the ease with which giant branch YORP break-up can generate binary asteroid subsystems is strongly dependent on internal strength. Formed binary subsystems in turn could be short-lived due to the resulting luminosity-enhanced binary YORP (BYORP) effect.

Photospheric nitrogen abundances and carbon 12C/13C ratios of red giant stars

Abstract Nitrogen abundances and carbon isotope ratios (12C$/$13C) in the atmospheres of red giants are known to be influenced by dredge-up of H-burning products, and serve as useful probes to study the nature of evolution-induced envelope mixing. We determined the [N/Fe] and 12C$/$13C ratios for 239 late-G/early-K giant stars by applying the spectrum-fitting technique to the 12CN and 13CN lines in the ∼8002–8005 Å region, with the aim of investigating how these quantities are related to other similar mixing-affected indicators which were already reported in our previous work. It was confirmed that [N/Fe] values are generally supersolar (typically by several tenths of a dex, though widely differing from star to star), anti-correlated with [C/Fe], and correlated with [Na/Fe], as expected from theory. As seen from their dependence upon stellar parameters, it appears that mixing tends to be enhanced with an increase of stellar luminosity (or mass) and rotational velocity, which is also reasonable from the theoretical viewpoint. In contrast, the resulting 12C$/$13C ratios turned out to be considerably diversified in the range of ∼5–50 (with a peak around ∼20), without showing any systematic dependence upon C or N abundance anomalies caused by the mixing of CN-cycled material. It thus appears that our understanding of the photospheric 12C$/$13C ratios in red giants is still incomplete, requiring more observational studies.

Stellar populations of galaxies in the ALHAMBRA survey up to z ∼ 1

Aims. We perform a comprehensive study of the stellar population properties (formation epoch, age, metallicity, and extinction) of quiescent galaxies as a function of size and stellar mass to constrain the physical mechanism governing the stellar mass assembly and the likely evolutive scenarios that explain their growth in size. Methods. After selecting all the quiescent galaxies from the ALHAMBRA survey by the dust-corrected stellar mass–colour diagram, we built a shared sample of ∼850 quiescent galaxies with reliable measurements of sizes from the HST. This sample is complete in stellar mass and luminosity, I ≤ 23. The stellar population properties were retrieved using the fitting code for spectral energy distributions called MUlti-Filter FITting for stellar population diagnostics (MUFFIT) with various sets of composite stellar population models. Age, formation epoch, metallicity, and extinction were studied on the stellar mass–size plane as function of size through a Monte Carlo approach. This accounted for uncertainties and degeneracy effects amongst stellar population properties. Results. The stellar population properties of quiescent galaxies and their stellar mass and size since z ∼ 1 are correlated. At fixed stellar mass, the more compact the quiescent galaxy, the older and richer in metals it is (1 Gyr and 0.1 dex, respectively). In addition, more compact galaxies may present slight lower extinctions than their more extended counterparts at the same stellar mass (< 0.1 mag). By means of studying constant regions of stellar population properties across the stellar mass–size plane, we obtained empirical relations to constrain the physical mechanism that governs the stellar mass assembly of the form M⋆ ∝ rcα, where α amounts to 0.50–0.55 ± 0.09. There are indications that support the idea that the velocity dispersion is tightly correlated with the stellar content of galaxies. The mechanisms driving the evolution of stellar populations can therefore be partly linked to the dynamical properties of galaxies, along with their gravitational potential.