DSpace Angular :: Browsing by Author "Chaname, Julio"

Browsing by Author "Chaname, Julio"

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A distant sample of halo wide binaries from SDSS
(2018) Coronado, Johanna; Paz Sepulveda, Maria; Gould, Andrew; Chaname, Julio
A megacam survey of outer halo satellites. VII. A single sersic index versus effective radius relation for milky way outer halo satellites
(2019) Marchi-Lasch, S.; Munoz, R.R.; Santana, F.A.; Carballo-Bello, J.A.; Chaname, Julio; Geha, M.; Simon, J.D.; Stetson, P.B.; Djorgovski, S.G.
A STARBURST IN THE CORE OF A GALAXY CLUSTER : THE DWARF IRREGULAR NGC 1427A IN FORNAX
(2015) Mora, Marcelo D.; Chaname, Julio; Puzia, Thomas H.
A Young, Low-density Stellar Stream in the Milky Way Disk: Theia 456
(2022) Andrews, Jeff J.; Curtis, Jason L.; Chaname, Julio; Agueros, Marcel A.; Schuler, Simon C.; Kounkel, Marina; Covey, Kevin R.
Our view of the variety of stellar structures pervading the local Milky Way has been transformed by the application of clustering algorithms to the Gaia catalog. In particular, several stellar streams have been recently discovered that are comprised of hundreds to thousands of stars and span several hundred parsecs. We analyze one such structure, Theia 456, a low-density stellar stream extending nearly 200 pc and 20 degrees across the sky. By supplementing Gaia astrometric data with spectroscopic metallicities from Large Sky Area Multi-Object Fiber Spectroscopic Telescope and photometric rotation periods from the Zwicky Transient Facility and the Transiting Exoplanet Survey Satellite, we establish Theia 456's radial velocity coherence, and we find strong evidence that members of Theia 456 have a common age (similar or equal to 175 Myr), common dynamical origin, and formed from chemically homogeneous prestellar material ([Fe/H] = -0.07 dex). Unlike well-known stellar streams in the Milky Way, which are in its halo, Theia 456 is firmly part of the thin disk. If our conclusions about Theia 456 can be applied to even a small fraction of the remaining similar or equal to 8300 independent structures in the Theia catalog, such low-density stellar streams may be ubiquitous. We comment on the implications this has for the nature of star formation throughout the Galaxy.
Are lithium-rich giants binaries? A radial velocity variability analysis of 1400 giants
(2024) Castro-Tapia, Matias; Aguilera-Gomez, Claudia; Chaname, Julio
Context. The existence of low-mass giants with large amounts of lithium (Li) in their surfaces has challenged stellar evolution for decades. One of the possibilities usually discussed in the literature to explain these Li-rich giants involves the interaction with a close binary companion, a scenario that predicts that, when compared against their non-enriched counterparts, Li-rich giants should preferentially be found as part of binary systems. Aims. We aim to assemble the largest possible sample of low-mass giants with well-measured Li abundances, to determine with high statistical significance the close binary fractions of Li-rich and Li-normal giants, and thus test the binary interaction scenario for the emergence of Li-rich giants. Methods. We developed a method that uses radial velocities (RVs) at three different epochs to quantify the degree of RV variability, which we used as a proxy for the presence of a close binary companion. The method was tested and calibrated against samples of known RV standard stars and known spectroscopic binaries. We then assembled a sample of 1418 giants with available RVs from RAVE, GALAH, and Gaia, as well as stellar parameters and Li abundances from GALAH, to which we applied our variability classification. We could determine an evolutionary state for 1030 of these giants. We also compared the results of our RV variability analysis with binarity indicators from the Gaia mission. Results. When applying our methodology to the control samples, we found that the accuracy of the classification is controlled by the precision of the RVs used in the analysis. For the set of RVs available for the giants, this accuracy is 80-85%. Consistent with seismic studies, the resulting sample of giants contains a fraction of Li-rich objects in the red clump (RC) that is twice as large as that in the first ascent red giant branch (RGB). Among RC giants, the fractions of Li-rich objects with a high RV variability and with no RV variability are the same as those for Li-normal objects, but we find some evidence that these fractions may be different for giants in the first-ascent RGB. Analysis of binary indicators in Gaia DR3 shows a smaller fraction of binary giants than our criteria, but no relation can be seen between Li enrichment and binarity either. Conclusions. Our RV variability analysis indicates that there is no preference for Li-rich giants in the RC to be part of binary systems, thus arguing against a binary interaction scenario for the genesis of the bulk of Li-rich giants at that evolutionary stage. On the other hand, Li-rich giants in the RGB appear to have a small but measurable preference for having close companions, something that deserves further scrutiny with more and better data. Additional measurements of the RVs of these giants at a higher RV precision would greatly help in confirming and more robustly quantifying these results.
Combining Astrometry and Elemental Abundances: The Case of the Candidate Pre-Gaia Halo Moving Groups G03-37, G18-39, and G21-22*
(2021) Schuler, Simon C.; Andrews, Jeff J.; Clanzy, Vincent R., II; Mourabit, Mohammed; Chaname, Julio; Agueros, Marcel A.
While most moving groups are young and nearby, a small number have been identified in the Galactic halo. Understanding the origin and evolution of these groups is an important piece of reconstructing the formation history of the halo. Here we report on our analysis of three putative halo moving groups: G03-37, G18-39, and G21-22. Based on Gaia EDR3 data, the stars associated with each group show some scatter in velocity (e.g., Toomre diagram) and integrals of motion (energy, angular momentum) spaces, counter to expectations of moving-group stars. We choose the best candidate of the three groups, G21-22, for follow-up chemical analysis based on high-resolution spectroscopy of six presumptive members. Using a new Python code that uses a Bayesian method to self-consistently propagate uncertainties from stellar atmosphere solutions in calculating individual abundances and spectral synthesis, we derive the abundances of alpha- (Mg, Si, Ca, Ti), Fe-peak (Cr, Sc, Mn, Fe, Ni), odd-Z (Na, Al, V), and neutron-capture (Ba, Eu) elements for each star. We find that the G21-22 stars are not chemically homogeneous. Based on the kinematic analysis for all three groups and the chemical analysis for G21-22, we conclude the three are not genuine moving groups. The case for G21-22 demonstrates the benefit of combining kinematic and chemical information in identifying conatal populations when either alone may be insufficient. Comparing the integrals of motion and velocities of the six G21-22 stars with those of known structures in the halo, we tentatively associate them with the Gaia-Enceladus accretion event.
Detection of the nearest Jupiter analogue in radial velocity and astrometry data
(2019) Feng, Fabo; Anglada Escudé, Guillem; Tuomi, Mikko; Jones, Hugh R. A.; Chaname, Julio; Butler, Paul R.; Janson, Markus
Discovery and Validation of a High-Density sub-Neptune from the K2 Mission
(2016) Espinoza Pérez, Néstor; Chanamé, Julio; Jordán Colzani, Andrés Cristóbal; Jenkins, James S.; Rojas, Felipe; Jofré, Paula; Mädler, Thomas; Rabus, Markus; Chaname, Julio; Pantoja, Blake; Soto, Maritza G.; Morzinski, Katie M.; Males, Jared R.; Ward-Duong, Kimberly; Close, Laird M.
Elevated r-process Enrichment in Gaia Sausage and Sequoia*
(2021) Aguado, David S.; Belokurov, Vasily; Myeong, G. C.; Evans, N. Wyn; Kobayashi, Chiaki; Sbordone, Luca; Chaname, Julio; Navarrete, Camila; Koposov, Sergey E.
The Gaia Sausage (GS) and the Sequoia represent the major accretion events that formed the stellar halo of the Milky Way. A detailed chemical study of these main building blocks provides a pristine view of the early steps of the Galaxy's assembly. We present the results of the analysis of the UVES high-resolution spectroscopic observations at the 8.2 m VLT of nine Sausage/Sequoia members selected kinematically using Gaia DR2. We season this set of measurements with archival data from Nissen & Schuster and GALAH DR3 (2020). Here, we focus on the neutron-capture process by analyzing Sr, Y, Ba, and Eu behavior. We detect clear enhancement in Eu abundance ([Eu/Fe] similar to 0.6-0.7) indicative of large prevalence of the r-process in the stellar n-capture makeup. We are also able to trace the evolution of the heavy element production across a wide range of metallicity. The barium to europium changes from a tight, flat sequence with [Ba/Eu] = -0.7 reflecting dominant contribution from exploding massive stars, to a clear upturn at higher iron abundances, betraying the onset of contamination from asymptotic giant branch (AGB) ejecta. Additionally, we discover two clear sequences in the [Fe/H]-[Ba/Fe] plane likely caused by distinct levels of s-process pollution and mixing within the GS progenitor.
Evidence of extra mixing in field giants as traced by the lithium and carbon isotope ratio
(2023) Aguilera-Gomez, Claudia; Jones, Matias I.; Chaname, Julio
Context. Although not predicted by standard stellar evolution, the surface abundance of light elements, such as lithium (Li), carbon, and nitrogen, changes during the red giant branch (RGB) as a result of extra mixing. This is usually associated with thermohaline mixing acting after the RGB bump. Peculiar Li-enriched RGB stars might also be related to either enhanced mixing or pollution from external sources.Aims. We measure the Li abundance and carbon isotopic ratio C-12/C-13 in a sample of 166 field red giants with -0.3 <= [Fe/H] <= 0.2, targeted by the EXPRESS radial velocity program to analyze the effects of extra mixing.Methods. We measured the abundances with spectral synthesis using high-quality spectra. Multiple-epoch observations needed for exoplanet detection were used to decrease the effects of telluric contamination in C-12/C-13 measurements.Results. Due to the prevalence of upper limits, the Li abundance pattern is complicated to interpret, but the comparison between RGB and core He-burning giants shows effects of mixing consistent with thermohaline. The most Li-enriched giant in the sample, classified as a RGB star close to the RGB bump, has low C-12/C-13. Given that the C-12/C-13 should not be affected by planet engulfment, this does not seem to be the source of the high Li. There is a decreasing correlation between mass and C-12/C-13 in the RGB and an increasing correlation in the horizontal branch, which, once again, is consistent with thermohaline mixing. Our data also show a correlation between C-12/C-13 and [Fe/H]. There is no evident impact of binarity either on Li or on C-12/C-13.Conclusions. Our sample shows behavior consistent with additional mixing acting after the RGB bump. The C-12/C-13 adds new clues which can be used to describe extra mixing, and it could well be the best tool to study mixing in giants. Additional measurements of C-12/C-13 in field stars would greatly improve our ability to compare data with models and understand mixing mechanisms.
Hubble Space Telescope proper motion (HSTPROMO) catalogs of galactic globular clusters. I. Sample selection, data reduction, and NGC 7078 results
(2014) Bellini, A.; Anderson, J.; Van Der Marel, R.; Watkins, L.; King, I.; Bianchini, P.; Chaname, Julio; Chandar, R.; Cool, A.; Ferraro, F.; Ford, H.; Massari, D.
Improved Constraints on the Initial-to-final Mass Relation of White Dwarfs Using Wide Binaries
(2021) Barrientos, Manuel; Chaname, Julio
We present observational constraints for the initial-to-final mass relation (IFMR) derived from 11 white dwarfs (WDs) in wide binaries (WBs) that contain a turnoff/subgiant primary. Because the components of WBs are coeval to a good approximation, the age of the WD progenitor can be determined from the study of its wide companion. However, previous works that used WBs to constrain the IFMR suffered from large uncertainties in the initial masses because their main-sequence primaries are difficult to age-date with good precision. Our selection of WBs with slightly evolved primaries avoids this problem by restricting to a region of parameter space where isochrone ages are significantly easier to determine with precision. The WDs of two of our originally selected binaries were found to be close double degenerates and are not used in the IFMR analysis. We obtained more precise constraints than existing ones in the mass range 1-2 M (circle dot), corresponding to a previously poorly constrained region of the IFMR. Having introduced the use of turnoff/subgiant-WD binaries, the study of the IFMR is not limited anymore by the precision in initial mass, but now the pressure is on final mass, i.e., the mass of the WD today. Looking at the full data set, our results would suggest a relatively large dispersion in the IFMR at low initial masses. More precise determinations of the mass of the WD components of our targets are necessary for settling this question.
Lithium abundance patterns of late-F stars: an in-depth analysis of the lithium desert
(2018) Aguilera Gómez, Claudia; Ramírez, Iván; Chaname, Julio
Mass Matters: No Evidence for Ubiquitous Lithium Production in Low-mass Clump Giants
(2022) Chaname, Julio; Pinsonneault, Marc H.; Aguilera-Gomez, Claudia; Zinn, Joel C.
Known sources of lithium (Li) in the universe include the Big Bang, novae, asymptotic giant branch stars, and cosmic-ray spallation. During their longer-lived evolutionary phases, stars are not expected to add to the Li budget of the Galaxy, but to largely deplete it. In this context, recent analyses of Li data from GALAH and LAMOST for field red clump (RC) stars have concluded that there is the need for a new production channel of Li, ubiquitous among low-mass stars, and that would be triggered on the upper red giant branch (RGB) or at helium ignition. This is distinct from the Li-rich giant problem and reflects bulk RC star properties. We provide an analysis of the GALAH Li data that accounts for the distribution of progenitor masses of field RC stars observed today. Such progenitors are different than today's field RGB stars. Using standard post-main-sequence stellar evolution, we show that the distribution of Li among field RC giants as observed by GALAH is consistent with standard model predictions, and does not require new Li production mechanisms. Our model predicts a large fraction of very low Li abundances from low-mass progenitors, with higher abundances from higher mass ones. Moreover, there should be a large number of upper limits for RC giants, and higher abundances should correspond to higher masses. The most recent GALAH data indeed confirm the presence of large numbers of upper limits, and a much lower mean Li abundance in RC stars, in concordance with our interpretation.
On collision course: The nature of the binary star cluster NGC2006/SL 538
(2019) Mora, Marcelo D.; Puzia, Thomas H.; Chaname, Julio
On Lithium-rich Red Giants : Engulfment on the Giant Branch of Trumpler 20
(2016) Aguilera Gomez, Claudia; Chaname, Julio; Pinsonneault, Marc H.; Joleen, K. Carlberg
On Lithium-Rich Red Giants. I. Engulfment of Sub-Stellar Companions
(2016) Aguilera Gómez, C.; Chaname, Julio
On the identification of wide binaries in the Kepler field
(2018) Godoy-Rivera, Diego; Chaname, Julio
Star cluster complexes in NGC 1427A
(2014) Mora, M.; Chaname, Julio; Puzia, Thomas H.
Substructure, supernovae, and a time-resolved star formation history for Upper Scorpius
(2023) Briceno-Morales, Geovanny; Chaname, Julio
The improved astrometry precision of Gaia-eDR3 allows us to perform a detailed study of the Upper Scorpius OB association and revisit its spatial, kinematic, and age substructure. We achieve this by combining clustering techniques and complementing with age estimations based on Gaia photometry. Our census retrieves 3661 candidate members for Upper Scorpius with contamination similar to 9 per cent. We also extract an astrometrically clean sample of 3004 sources with contamination similar to 6 per cent. We show that Upper Scorpius can be divided into at least three main kinematic groups. We systematically investigate and characterize the Upper Scorpius' internal structure, revealing that at least similar to 34 per cent of its stellar populations are contained in seven spatial substructures, with well defined boundaries, kinematics, and relative ages with suggested names: pi Scorpii (20(+/- 1)(+/- 2) Myr), alpha Scorpii (14(+/- 1)(+/- 2) Myr), delta Scorpii (9(+/- 1)(+/- 2) Myr), beta Scorpii (8(+/- 1)(+/- 1) Myr), omega Scorpii (8(+/- 1)(+/- 1) Myr), nu Scorpii (7(+/- 1)(+/- 1)Myr), after their brightest member, and the well known rho Ophiuchi (4(+/- 1)(+/- 1) Myr). We find a clear correlation in (1) density-age, providing an empirical expansion law to be tested in other associations, and (2) tangential velocity-age, providing constrains on the dynamics of these substructures and the position of potential past triggering events. We estimate the time at which four potential supernovae events occurred in Upper Scorpius. Based on these findings, we tie together previous work on the region and suggest a star formation history with unprecedented temporal resolution.

Browsing by Author "Chaname, Julio"

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