Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCarbon star formation as seen through the non-monotonic initial-final mass relation
77
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The initial-final mass relation (IFMR) links the birth mass of a star to the mass of the compact remnant left at its death. While the relevance of the IFMR across astrophysics is universally acknowledged, not all of its fine details have yet been resolved. A new analysis of a few carbon-oxygen white dwarfs in old open clusters of the Milky Way led us to identify a kink in the IFMR, located over a range of initial masses, $1.65 lesssim M_{rm i}/M_{odot} lesssim 2.10$. The kinks peak in WD mass of $approx 0.70-0.75 , M_{odot}$ is produced by stars with $M_{rm i} simeq 1.8 - 1.9 , M_{odot}$, corresponding to ages of about $1.8 - 1.7 $ Gyr. Interestingly, this peak coincides with the initial mass limit between low-mass stars that develop a degenerate helium core after central hydrogen exhaustion, and intermediate-mass stars that avoid electron degeneracy. We interpret the IFMR kink as the signature of carbon star formation in the Milky Way. This finding is critical to constraining the evolution and chemical enrichment of low-mass stars, and their impact on the spectrophotometric properties of galaxies.
rate research
Read More
We present the preliminary results of a survey of the open clusters NGC3532 and NGC2287 for new white dwarf members which can help improve understanding of the form of the upper end of the stellar initial mass-final mass relation. We identify four objects with cooling times, distances and proper motions consistent with membership of these clusters. We find that despite a range in age of ~100Myr the masses of the four heaviest white dwarfs in NGC3532 span the narrow mass interval M~0.9-1.0Msolar suggesting that the initial mass-final mass relation is relatively flatter over 4.5Msolar <~ M_init <~ 6.5Msolar than at immediately lower masses. Additionally, we have unearthed WD J0646-203 which is possibly the most massive cluster white dwarf identified to date. With M~1.1Msolar it seems likely to be composed of ONe and has a cooling time consistent with it having evolved from a single star.
The initial-final mass relation (IFMR) represents the total mass lost by a star during the entirety of its evolution from the zero age main sequence to the white dwarf cooling track. The semi-empirical IFMR is largely based on observations of DA white dwarfs, the most common spectral type of white dwarf and the simplest atmosphere to model. We present a first derivation of the semi-empirical IFMR for hydrogen deficient white dwarfs (non-DA) in open star clusters. We identify a possible discrepancy between the DA and non-DA IFMRs, with non-DA white dwarfs $approx 0.07 M_odot$ less massive at a given initial mass. Such a discrepancy is unexpected based on theoretical models of non-DA formation and observations of field white dwarf mass distributions. If real, the discrepancy is likely due to enhanced mass loss during the final thermal pulse and renewed post-AGB evolution of the star. However, we are dubious that the mass discrepancy is physical and instead is due to the small sample size, to systematic issues in model atmospheres of non-DAs, and to the uncertain evolutionary history of Procyon B (spectral type DQZ). A significantly larger sample size is needed to test these assertions. In addition, we also present Monte Carlo models of the correlated errors for DA and non-DA white dwarfs in the initial-final mass plane. We find the uncertainties in initial-final mass determinations for individual white dwarfs can be significantly asymmetric, but the recovered functional form of the IFMR is grossly unaffected by the correlated errors.
We have undertaken a systematic study of pre-main sequence (PMS) stars spanning a wide range of masses (0.5 - 4 Msolar), metallicities (0.1 - 1 Zsolar) and ages (0.5 - 30 Myr). We have used the Hubble Space Telescope (HST) to identify and characterise a large sample of PMS objects in several star-forming regions in the Magellanic Clouds, namely 30 Dor and the SN 1987A field in the LMC, and NGC 346 and NGC 602 in the SMC, and have compared them to PMS stars in similar regions in the Milky Way, such as NGC 3603 and Trumpler 14, which we studied with the HST and Very Large Telescope (VLT). We have developed a novel method that combines broad-band (V, I) photometry with narrow-band Halpha imaging to determine the physical parameters (temperature, luminosity, age, mass and mass accretion rate) of more than 3000 bona-fide PMS stars still undergoing active mass accretion. This is presently the largest and most homogeneous sample of PMS objects with known physical properties and includes not only very young objects, but also PMS stars older than 10 - 20 Myr that are approaching the main sequence (MS). We find that the mass accretion rate scales roughly with the square root of the age, with the mass of the star to the power of 1.5, and with the inverse of the cube root of the metallicity. The mass accretion rates for stars of the same mass and age are thus systematically higher in the Magellanic Clouds than in the Milky Way. These results are bound to have important implications for, and constraints on our understanding of the star formation process.
We study the star-formation history of the Galactic bulge, as derived from the age distribution of the central stars of planetary nebulae that belong to this stellar population. The high resolution imaging and spectroscopic observations of 31 compact planetary nebulae are used to derive their central star masses. The Bloecker tracks with the cluster IFMR result in ages, which are unexpectedly young. We find that the Bloecker post-AGB tracks need to be accelerated by a factor of three to fit the local white dwarf masses. This acceleration extends the age distribution. We adjust the IFMR as a free parameter to map the central star ages on the full age range of bulge stellar populations. This fit requires a steeper IFMR than the cluster relation. We find a star-formation rate in the Galactic bulge, which is approximately constant between 3 and 10 Gyr ago. The result indicates that planetary nebulae are mainly associated with the younger and more metal-rich bulge populations. The constant rate of star-formation between 3 and 10 Gyr agrees with suggestions that the metal-rich component of the bulge is formed during an extended process, such as a bar interaction.
The initial-final mass relation (IFMR) of white dwarfs (WDs) plays an important role in stellar evolution. To derive precise estimates of IFMRs and explore how they may vary among star clusters, we propose a Bayesian hierarchical model that pools photo- metric data from multiple star clusters. After performing a simulation study to show the benefits of the Bayesian hierarchical model, we apply this model to five star clus- ters: the Hyades, M67, NGC 188, NGC 2168, and NGC 2477, leading to reasonable and consistent estimates of IFMRs for these clusters. We illustrate how a cluster-specific analysis of NGC 188 using its own photometric data can produce an unreasonable IFMR since its WDs have a narrow range of zero-age main sequence (ZAMS) masses. However, the Bayesian hierarchical model corrects the cluster-specific analysis by bor- rowing strength from other clusters, thus generating more reliable estimates of IFMR parameters. The data analysis presents the benefits of Bayesian hierarchical modelling over conventional cluster-specific methods, which motivates us to elaborate the pow- erful statistical techniques in this article.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
