scholarly journals Occurrence rates of small planets from HARPS

2020 ◽  
Vol 643 ◽  
pp. A106
Author(s):  
D. Bashi ◽  
S. Zucker ◽  
V. Adibekyan ◽  
N. C. Santos ◽  
L. Tal-Or ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Detection Limits ◽  
Thick Disk ◽  
Occurrence Rate ◽  
Mass Detection ◽  
The Galaxy ◽  
Low Mass ◽  
Thin And Thick Disks ◽  
Thick Disks ◽  
Stellar Properties

Context. The stars in the Milky Way thin and thick disks can be distinguished by several properties such as metallicity and kinematics. It is not clear whether the two populations also differ in the properties of planets orbiting the stars. In order to study this, a careful analysis of both the chemical composition and mass detection limits is required for a sufficiently large sample. Currently, this information is still limited only to large radial-velocity (RV) programs. Based on the recently published archival database of the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph, we present a first analysis of low-mass (small) planet occurrence rates in a sample of thin- and thick-disk stars. Aims. We aim to assess the effects of stellar properties on planet occurrence rates and to obtain first estimates of planet occurrence rates in the thin and thick disks of the Galaxy. As a baseline for comparison, we also aim to provide an updated value for the small close-in planet occurrence rate and compare it with the results of previous RV and transit (Kepler) works. Methods. We used archival HARPS RV datasets to calculate detection limits of a sample of stars that were previously analysed for their elemental abundances. For stars with known planets we first subtracted the Keplerian orbit. We then used this information to calculate planet occurrence rates according to a simplified Bayesian model in different regimes of stellar and planet properties. Results. Our results suggest that metal-poor stars and more massive stars host fewer low-mass close-in planets. We find the occurrence rates of these planets in the thin and thick disks to be comparable. In the iron-poor regimes, we find these occurrence rates to be significantly larger at the high-α region (thick-disk stars) as compared with the low-α region (thin-disk stars). In general, we find the average number of close-in small planets (2–100 days, 1–20M⊕) per star (FGK-dwarfs) to be: n¯p = 0.36 ± 0.05, while the fraction of stars with planets is Fh = 0.23−0.03+0.04. Qualitatively, our results agree well with previous estimates based on RV and Kepler surveys. Conclusions. This work provides a first estimate of the close-in small planet occurrence rates in the solar neighbourhood of the thin and thick disks of the Galaxy. It is unclear whether there are other stellar properties related to the Galactic context that affect small-planet occurrence rates, or if it is only the combined effects of stellar metal content and mass. A future larger sample of stars and planets is needed to address those questions.

scholarly journals The chemical fingerprints of the thin and the thick disk

2008 ◽  
Vol 4 (S254) ◽  
pp. 197-202
Author(s):  
Sofia Feltzing ◽  
Sally Oey ◽  
Thomas Bensby
Keyword(s):  
Past History ◽  
Thick Disk ◽  
Chemical Abundance ◽  
Dwarf Stars ◽  
Abundance Patterns ◽  
The Galaxy ◽  
Thin And Thick Disks ◽  
Thick Disks ◽  
Definition Of ◽  
Galactic Stellar Populations

AbstractThe past history and origin of the different Galactic stellar populations are manifested in their different chemical abundance patterns. We obtained new elemental abundances for 553 F and G dwarf stars, to more accurately quantify these patterns for the thin and thick disks. However, the exact definition of disk membership is not straightforward. Stars that have a high likelihood of belonging to the thin disk show different abundance patterns from those for the thick disk. In contrast, we show that stars for the Hercules Stream do not show unique abundance patterns, but rather follow those of the thin and thick disks. This strongly suggests that the Hercules Stream is a feature induced by internal dynamics within the Galaxy rather than the remnant of an accreted satellite.

scholarly journals Kinematical & Chemical Characteristics of the Thin and Thick Disks

2008 ◽  
Vol 4 (S254) ◽  
pp. 179-190 ◽  
Author(s):  
Rosemary F. G. Wyse
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Milky Way ◽  
Observational Evidence ◽  
Chemical Characteristics ◽  
Chemical Abundance ◽  
The Galaxy ◽  
History Of ◽  
Thin And Thick Disks ◽  
Thick Disks

AbstractI discuss how the chemical abundance distributions, kinematics and age distributions of stars in the thin and thick disks of the Galaxy can be used to decipher the merger history of the Milky Way, a typical large galaxy. The observational evidence points to a rather quiescent past merging history, unusual in the context of the ‘consensus’ cold-dark-matter cosmology favoured from observations of structure on scales larger than individual galaxies.

scholarly journals The radial extent of the Galactic thick disk

2016 ◽  
Vol 11 (S321) ◽  
pp. 3-5
Author(s):  
Thomas Bensby
Keyword(s):  
Milky Way ◽  
Galactic Disk ◽  
Thin Disk ◽  
Thick Disk ◽  
Stellar Disk ◽  
Chemical Signatures ◽  
Radial Extent ◽  
Thin And Thick Disks ◽  
Thick Disks ◽  
Scale Length

AbstractBased on observational data from the fourth internal data release of the Gaia-ESO Survey we probe the abundance structure in the Milky Way stellar disk as a function of galactocentric radius and height above the plane. We find that the inner and outer Galactic disks have different chemical signatures. The stars in the inner Galactic disk show abundance signatures of both the thin and thick disks, while the stars in the outer Galactic disk resemble in majority the abundances seen in the thin disk. Assuming that the Galactic thick disk can be associated with the α-enriched population, this can be interpreted as that the thick disk density drops drastically beyond a galactocentric radius of about 10 kpc. This is in agreement with recent findings that the thick disk has a short scale-length, shorter than that of the the thin disk.

scholarly journals The ESO supernovae type Ia progenitor survey (SPY)

2020 ◽  
Vol 638 ◽  
pp. A131 ◽  
Author(s):  
R. Napiwotzki ◽  
C. A. Karl ◽  
T. Lisker ◽  
S. Catalán ◽  
H. Drechsel ◽  
...  
Keyword(s):  
Radial Velocity ◽  
White Dwarfs ◽  
Binary Systems ◽  
Detection Efficiency ◽  
Close Binary ◽  
The Galaxy ◽  
Type Ia ◽  
Low Mass ◽  
Kinematic Studies ◽  
Ia Supernovae

Close double degenerate binaries are one of the favoured progenitor channels for type Ia supernovae, but it is unclear how many suitable systems there are in the Galaxy. We report results of a large radial velocity survey for double degenerate (DD) binaries using the UVES spectrograph at the ESO VLT (ESO SN Ia Progenitor surveY – SPY). Exposures taken at different epochs are checked for radial velocity shifts indicating close binary systems. We observed 689 targets classified as DA white dwarfs (displaying hydrogen-rich atmospheres), of which 46 were found to possess a cool companion. We measured radial velocities (RV) of the remaining 643 DA white dwarfs. We managed to secure observations at two or more epochs for 625 targets, supplemented by eleven objects meeting our selection criteria from literature. The data reduction and analysis methods applied to the survey data are described in detail. The sample contains 39 double degenerate binaries, only four of which were previously known. Twenty are double-lined systems, in which features from both components are visible, the other 19 are single-lined binaries. We provide absolute RVs transformed to the heliocentric system suitable for kinematic studies. Our sample is large enough to sub-divide by mass: 16 out of 44 low mass targets (≤0.45 M⊙) are detected as DDs, while just 23 of the remaining 567 targets with multiple spectra and mass > 0.45 M⊙ are double. The detected fraction amongst the low mass objects (36.4 ± 7.3%) is significantly higher than for the higher-mass, carbon-oxygen core dominated part of the sample (3.9 ± 0.8%), but it is much lower than expected from the detection efficiency for companion masses of 0.05 M⊙ or higher and a 100% binary fraction. This suggests either companion stars of with a mass below 0.05 M⊙ or some of the low mass white dwarfs are single.

scholarly journals The Chemical Composition of the Galactic Bulge and Implications for its Evolution

2016 ◽  
Vol 33 ◽  
Author(s):  
Andrew McWilliam
Keyword(s):  
Time Delay ◽  
Chemical Composition ◽  
Measurement Errors ◽  
Thick Disk ◽  
Core Collapse ◽  
Vertical Scale ◽  
Effective Yield ◽  
Type Ia ◽  
Thin And Thick Disks ◽  
Thick Disks

AbstractAt a bulge latitude of b = −4°, the average [Fe/H] and [Mg/H] values are +0.06 and +0.17 dex, roughly 0.2 and 0.7 dex higher than the local thin and thick disk values, respectively, suggesting a large bulge effective yield, perhaps due to efficient retention of supernova ejecta.The bulge vertical [Fe/H] gradient, at ~ 0.5 dex/kpc, appears to be due to a changing mixture of sub-populations (near +0.3 dex and −0.3 dex and one possibly near −0.7 dex) with latitude. At solar [Fe/H], the bulge [Al/Fe] and [α/Fe] ratios are ~ +0.15 dex. Below [Fe/H] < ![CDATA[$ ~ −0.5 dex, the bulge and local thick disk compositions are very similar; but the measured [Mg/Fe], [⟨SiCaTi⟩/Fe], [La/Eu] and dramatic [Cu/Fe] ratios suggest higher SFR in the bulge. However, these composition differences with the thick disk could be due to measurement errors and non-LTE effects.Unusual zig-zag trends of [Cu/Fe] and [Na/Fe] suggest metallicity-dependent nucleosynthesis by core-collapse supernovae in the Type Ia supernova time-delay scenario.The bulge sub-population compositions resemble the local thin and thick disks, but at higher [Fe/H], suggesting a radial [Fe/H] gradient of − $0.04]] > to − 0.05 dex/kpc for both the thin and thick disks. If the bulge formed through accretion of inner thin and thick disk stars, it appears that these stars retained vertical scale heights characteristic of their kinematic origin, resulting in the vertical [Fe/H] gradient and [α/Fe] trends seen today.

scholarly journals Contribution of HI-bearing ultra-diffuse galaxies to the cosmic number density of galaxies

2018 ◽  
Vol 614 ◽  
pp. A21 ◽  
Author(s):  
M. G. Jones ◽  
E. Papastergis ◽  
V. Pandya ◽  
L. Leisman ◽  
A. J. Romanowsky ◽  
...  
Keyword(s):  
Mass Density ◽  
Mass Function ◽  
Occurrence Rate ◽  
Slow Rotation ◽  
Number Density ◽  
Spin Parameter ◽  
The Galaxy ◽  
Order Of Magnitude ◽  
Low Mass ◽  
Star Formation Histories

We estimate the cosmic number density of the recently identified class of HI-bearing ultra-diffuse sources (HUDs) based on the completeness limits of the ALFALFA survey. These objects have HI masses approximately in the range 8.5 < logMHI∕M⊙ < 9.5, average r-band surface brightnesses fainter than 24 mag arcsec−2, half-light radii greater than 1.5 kpc, and are separated from neighbours by at least 350 kpc. In this work we demonstrate that they contribute at most ~6% of the population of HI-bearing dwarfs detected by ALFALFA (with similar HI masses), have a total cosmic number density of (1.5 ± 0.6) × 10−3 Mpc−3, and an HI mass density of (6.0 ± 0.8) × 105 M⊙ Mpc−3. We estimate that this is similar to the total cosmic number density of ultra-diffuse galaxies (UDGs) in groups and clusters, and conclude that the relation between the number of UDGs hosted in a halo and the halo mass must have a break below M200 ~ 1012 M⊙ in order to account for the abundance of HUDs in the field. The distribution of the velocity widths of HUDs rises steeply towards low values, indicating a preference for slow rotation rates compared to the global HI-rich dwarf population. These objects were already included in previous measurements of the HI mass function, but have been absent from measurements of the galaxy stellar mass function owing to their low surface brightness. However, we estimate that due to their low number density the inclusion of HUDs would constitute a correction of less than 1%. Comparison with the Santa Cruz semi-analytic model shows that it produces HI-rich central UDGs that have similar colours to HUDs, but that these UDGs are currently produced in a much greater number. While previous results from this sample have favoured formation scenarios where HUDs form in high spin-parameter halos, comparisons with recent results which invoke that formation mechanism reveal that this model produces an order of magnitude more field UDGs than we observe in the HUD population, and these have an occurrence rate (relative to other dwarfs) that is approximately double what we observe. In addition, the colours of HUDs are bluer than predicted, although we suspect this is due to a systematic problem in reproducing the star formation histories of low-mass galaxies rather than being specific to the ultra-diffuse nature of these sources.

scholarly journals Resolving the stellar outskirts of six Milky Way-like galaxies beyond the Local Group

2016 ◽  
Vol 11 (S321) ◽  
pp. 43-43
Author(s):  
A. Monachesi ◽  
E. F. Bell ◽  
D. J. Radburn-Smith ◽  
B. Harmsen ◽  
R. S. de Jong ◽  
...  
Keyword(s):  
Galaxy Formation ◽  
Milky Way ◽  
Local Group ◽  
Spiral Galaxies ◽  
Disk Galaxies ◽  
Galaxy Halos ◽  
Model Predictions ◽  
The Galaxy ◽  
Thick Disks ◽  
Stellar Properties

AbstractModels of galaxy formation in a hierarchical universe predict substantial scatter in the halo-to-halo stellar properties, owing to stochasticity in galaxies’ merger histories. Currently, only few detailed observations of galaxy’s halos are available, mainly for the Milky Way and M31. The Galaxy Halos, Outer disks, Substructure, Thick disks and Star clusters (GHOSTS) HST survey is the largest study to date of the resolved stellar populations in the outskirts of disk galaxies and its observations offer a direct test of model predictions. Here we present the results we obtain for six highly inclined nearby Milky Way-mass spiral galaxies. We find a great diversity in the properties of their stellar halos.

scholarly journals Analysis of neutron capture elements in thin and thick disks of the Galaxy

2011 ◽  
Author(s):  
Tamara Mishenina ◽  
Tatiana Gorbaneva ◽  
Nikos Prantzos ◽  
C. Soubiran ◽  
Nina Basak
Keyword(s):  
Neutron Capture ◽  
The Galaxy ◽  
Thin And Thick Disks ◽  
Thick Disks

scholarly journals Abundances of disk and bulge giants from high-resolution optical spectra

2019 ◽  
Vol 625 ◽  
pp. A141 ◽  
Author(s):  
M. Lomaeva ◽  
H. Jönsson ◽  
N. Ryde ◽  
M. Schultheis ◽  
B. Thorsbro
Keyword(s):  
High Resolution ◽  
Chemical Evolution ◽  
Galaxy Formation ◽  
Signal To Noise Ratio ◽  
Optical Spectra ◽  
Thick Disk ◽  
Thin And Thick Disks ◽  
Thick Disks ◽  
Local Disk ◽  
K Giants

Context. The formation and evolution of the Galactic bulge and the Milky Way is still a debated subject. Observations of the X-shaped bulge, cylindrical stellar motions, and the presumed existence of a fraction of young stars in the bulge have suggested that it formed through secular evolution of the disk and not through gas dissipation and/or mergers, as thought previously. Aims. Our goal was to measure the abundances of six iron-peak elements (Sc, V, Cr, Mn, Co, and Ni) in the local thin and thick disks and in the bulge. These abundances can provide additional observational constraints for Galaxy formation and chemical evolution models, and help us to understand whether the bulge has emerged from the thick disk or not. Methods. We use high-resolution optical spectra of 291 K giants in the local disk mostly obtained by the FIES at NOT (signal-to-noise ratio (S/N) of 80–100) and 45 K giants in the bulge obtained by the UVES/FLAMES at VLT (S/N of 10–80). The abundances are measured using Spectroscopy Made Easy (SME). Additionally, we apply non-local thermodynamic equilibrium corrections to the ratios [Mn/Fe] and [Co/Fe]. The thin and thick disks were separated according to their metallicity, [Ti/Fe], as well as proper motions and the radial velocities from Gaia DR2. Results. The trend of [V/Fe] vs. [Fe/H] shows a separation between the disk components, being more enhanced in the thick disk. Similarly, the [Co/Fe] vs. [Fe/H] trend shows a hint of an enhancement in the local thick disk. The trends of V and Co in the bulge appear to be even more enhanced, although within the uncertainties. The decreasing value of [Sc/Fe] with increasing metallicity is observed in all the components, while our [Mn/Fe] value steadily increases with increasing metallicity in the local disk and the bulge instead. For Cr and Ni we find a flat trend following iron for the whole metallicity range in the disk and the bulge. The ratio of [Ni/Fe] appears slightly overabundant in the thick disk and the bulge compared to the thin disk, although the difference is minor. Conclusions. The somewhat enhanced ratios of [V/Fe] and [Co/Fe] observed in the bulge suggest that the local thick disk and the bulge might have experienced different chemical enrichment and evolutionary paths. However, we are unable to predict the exact evolutionary path of the bulge solely based on these observations. Galactic chemical evolution models could, on the other hand, allow us to predict them using these results.

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