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Showing 1-18 of about 18 results.
Multiple Stellar Populations in Asymptotic Giant Branch Stars of Galactic Globular ClustersLagioia, E. P.Milone, A. P.Marino, A. F.Tailo, M.Renzini, A.Carlos, M.Cordoni, G.Dondoglio, E.Jang, S.Karakas, A.Dotter, AaronDOI: info:10.3847/1538-4357/abdfcfv. 9106
Lagioia, E. P., Milone, A. P., Marino, A. F., Tailo, M., Renzini, A., Carlos, M., Cordoni, G., Dondoglio, E., Jang, S., Karakas, A., and Dotter, Aaron. 2021. "Multiple Stellar Populations in Asymptotic Giant Branch Stars of Galactic Globular Clusters." The Astrophysical Journal 910:6. https://doi.org/10.3847/1538-4357/abdfcf
ID: 159440
Type: article
Authors: Lagioia, E. P.; Milone, A. P.; Marino, A. F.; Tailo, M.; Renzini, A.; Carlos, M.; Cordoni, G.; Dondoglio, E.; Jang, S.; Karakas, A.; Dotter, Aaron
Abstract: Multiple stellar populations (MPs) are a distinct characteristic of globular clusters (GCs). Their general properties have been widely studied among main-sequence, red giant branch (RGB), and horizontal branch (HB) stars, but a common framework is still missing at later evolutionary stages. We studied the MP phenomenon along the asymptotic giant branch (AGB) sequences in 58 GCs, observed with the Hubble Space Telescope in UV and optical filters. Using UV-optical color-magnitude diagrams, we selected the AGB members of each cluster and identified the AGB candidates of the metal-enhanced population in type II GCs. We studied the photometric properties of the AGB stars and compared them to theoretical models derived from synthetic spectral analysis. We observed the following features: (i) the spread of AGB stars in photometric indices sensitive to variations of light elements and helium is typically larger than that expected from photometric errors; (ii) the fraction of metal-enhanced stars in the AGB is lower than that in the RGB in most of the type II GCs; (iii) the fraction of 1G stars derived from the chromosome map of AGB stars in 15 GCs is larger than that of RGB stars; and (v) the AGB/HB frequency correlates with the average mass of the most helium-enriched population. These findings represent clear evidence of the presence of MPs along the AGB of Galactic GCs and indicate that a significant fraction of helium-enriched stars, which have lower mass in the HB, do not evolve to the AGB phase, leaving the HB sequence toward higher effective temperatures, as predicted by the AGB manqué scenario.
MINESweeper: Spectrophotometric Modeling of Stars in the Gaia EraCargile, Phillip A.Conroy, CharlieJohnson, Benjamin D.Ting, Yuan-SenBonaca, AnaDotter, AaronSpeagle, Joshua S.DOI: info:10.3847/1538-4357/aba43bv. 90028
Cargile, Phillip A., Conroy, Charlie, Johnson, Benjamin D., Ting, Yuan-Sen, Bonaca, Ana, Dotter, Aaron, and Speagle, Joshua S. 2020. "MINESweeper: Spectrophotometric Modeling of Stars in the Gaia Era." The Astrophysical Journal 900:28. https://doi.org/10.3847/1538-4357/aba43b
ID: 157673
Type: article
Authors: Cargile, Phillip A.; Conroy, Charlie; Johnson, Benjamin D.; Ting, Yuan-Sen; Bonaca, Ana; Dotter, Aaron; Speagle, Joshua S.
Abstract: We present MINESweeper, a tool to measure stellar parameters by jointly fitting observed spectra and broadband photometry to model isochrones and spectral libraries. This approach enables the measurement of spectrophotometric distances, in addition to stellar parameters such as Teff, $\mathrm{log}g$, [Fe/H], [α/Fe], and radial velocity. MINESweeper employs a Bayesian framework and can easily incorporate a variety of priors, including Gaia parallaxes. Mock data are fit in order to demonstrate how the precision of derived parameters depends on evolutionary phase and signal-to-noise ratio. We then fit a selection of data in order to validate the model outputs. Fits to a variety of benchmark stars including Procyon, Arcturus, and the Sun result in derived stellar parameters that are in good agreement with the literature. We then fit combined spectra and photometry of stars in the open and globular clusters M92, M13, M3, M107, M71, and M67. Derived distances, [Fe/H], [α/Fe], and $\mathrm{log}g$-Teff relations are in overall good agreement with literature values, although there are trends between metallicity and $\mathrm{log}g$ within clusters that point to systematic uncertainties at the ≍0.1 dex level. Finally, we fit a large sample of stars from the H3 Spectroscopic Survey in which high-quality Gaia parallaxes are also available. These stars are fit without the Gaia parallaxes so that the geometric parallaxes can serve as an independent test of the spectrophotometric distances. Comparison between the two reveals good agreement within their formal uncertainties after accounting for the Gaia zero-point uncertainties.
Erratum: 'A Complete Census of Luminous Stellar Variability on Day to Decade Timescales' (2018, ApJ, 864, 111)Conroy, CharlieStrader, Jayvan Dokkum, PieterDolphin, Andrew E.Weisz, Daniel R.Murphy, Jeremiah W.Dotter, AaronJohnson, Benjamin D.Cargile, PhillipDOI: info:10.3847/1538-4357/ab75f1v. 891102
Conroy, Charlie, Strader, Jay, van Dokkum, Pieter, Dolphin, Andrew E., Weisz, Daniel R., Murphy, Jeremiah W., Dotter, Aaron, Johnson, Benjamin D., and Cargile, Phillip. 2020. "Erratum: "A Complete Census of Luminous Stellar Variability on Day to Decade Timescales" (2018, ApJ, 864, 111)." The Astrophysical Journal 891:102. https://doi.org/10.3847/1538-4357/ab75f1
ID: 158089
Type: article
Authors: Conroy, Charlie; Strader, Jay; van Dokkum, Pieter; Dolphin, Andrew E.; Weisz, Daniel R.; Murphy, Jeremiah W.; Dotter, Aaron; Johnson, Benjamin D.; Cargile, Phillip
Extended main sequence turnoffs in open clusters as seen by Gaia - II. The enigma of NGC 2509de Juan Ovelar, M.Gossage, SethKamann, S.Bastian, N.Usher, C.Cabrera-Ziri, IvanDotter, AaronConroy, CharlieLardo, C.DOI: info:10.1093/mnras/stz3128v. 4912129–2136
de Juan Ovelar, M., Gossage, Seth, Kamann, S., Bastian, N., Usher, C., Cabrera-Ziri, Ivan, Dotter, Aaron, Conroy, Charlie, and Lardo, C. 2020. "Extended main sequence turnoffs in open clusters as seen by Gaia - II. The enigma of NGC 2509." Monthly Notices of the Royal Astronomical Society 491:2129– 2136. https://doi.org/10.1093/mnras/stz3128
ID: 155707
Type: article
Authors: de Juan Ovelar, M.; Gossage, Seth; Kamann, S.; Bastian, N.; Usher, C.; Cabrera-Ziri, Ivan; Dotter, Aaron; Conroy, Charlie; Lardo, C.
Abstract: We investigate the morphology of the colour-magnitude diagram (CMD) of the open cluster NGC 2509 in comparison with other Galactic open clusters of similar age using Gaia photometry. At ∼900 {Myr} Galactic open clusters in our sample all show an extended main sequence turnoff (eMSTO) with the exception of NGC 2509, which presents an exceptionally narrow CMD. Our analysis of the Gaia data rules out differential extinction, stellar density, and binaries as a cause for the singular MSTO morphology in this cluster. We interpret this feature as a consequence of the stellar rotation distribution within the cluster and present the analysis with MESA Isochrones and Stellar Tracks (MIST) stellar evolution models that include the effect of stellar rotation on which we based our conclusion. In particular, these models point to an unusually narrow range of stellar rotation rates (Ω/Ωcrit, ZAMS = [0.4, 0.6]) within the cluster as the cause of this singular feature in the CMD of NGC 2509. Interestingly, models that do not include rotation are not as good at reproducing the morphology of the observed CMD in this cluster.
Asteroseismic Modeling of Gravity Modes in Slowly Rotating A/F Stars with Radiative LevitationMombarg, Joey S. G.Dotter, Aaronvan Reeth, TimothyTkachenko, AndrewGebruers, SarahAerts, ConnyDOI: info:10.3847/1538-4357/ab8d36v. 89551
Mombarg, Joey S. G., Dotter, Aaron, van Reeth, Timothy, Tkachenko, Andrew, Gebruers, Sarah, and Aerts, Conny. 2020. "Asteroseismic Modeling of Gravity Modes in Slowly Rotating A/F Stars with Radiative Levitation." The Astrophysical Journal 895:51. https://doi.org/10.3847/1538-4357/ab8d36
ID: 156888
Type: article
Authors: Mombarg, Joey S. G.; Dotter, Aaron; van Reeth, Timothy; Tkachenko, Andrew; Gebruers, Sarah; Aerts, Conny
Abstract: It has been known for several decades that transport of chemical elements is induced by the process of microscopic atomic diffusion. Yet the effect of atomic diffusion, including radiative levitation, has hardly been studied in the context of gravity-mode pulsations of core hydrogen burning stars. In this paper we study the difference in the properties of such modes for models with and without atomic diffusion. We perform asteroseismic modeling of two slowly rotating A- and F-type pulsators, KIC 11145123 ( ${f}_{\mathrm{rot}}$ $\approx \,0.010\,{\mathrm{day}}^{-1}$ ) and KIC 9751996 ( ${f}_{\mathrm{rot}}$ $\approx \,0.0696\,{\mathrm{day}}^{-1}$ ), respectively, based on the periods of individual gravity modes. For both stars, we find models whose g-mode periods are in very good agreement with the Kepler asteroseismic data, keeping in mind that the theoretical/numerical precision of present-day stellar evolution models is typically about two orders of magnitude lower than the measurement errors. Using the Akaike Information Criterion, we have made a comparison between our best models with and without diffusion and found very strong evidence for signatures of atomic diffusion in the pulsations of KIC 11145123. In the case of KIC 9751996 the models with atomic diffusion are not able to explain the data as well as the models without it. Furthermore, we compare the observed surface abundances with those predicted by the best-fitting models. The observed abundances are inconclusive for KIC 9751996, while those of KIC 11145123 from the literature can better be explained by a model with atomic diffusion.
The Cluster AgeS Experiment (CASE) - VIII. Age and distance of the Globular Cluster 47 Tuc from the analysis of two detached eclipsing binariesThompson, I. B.Udalski, A.Dotter, AaronRozyczka, M.Schwarzenberg-Czerny, A.Pych, W.Beletsky, Y.Burley, G. S.Marshall, J. L.McWilliam, A.Morrell, N.Osip, D.Monson, A.Persson, S. E.Szymański, M. K.Soszyński, I.Poleski, R.Ulaczyk, K.Wyrzykowski, Ł.Kozłowski, S.Mróz, P.Pietrukowicz, P.Skowron, J.DOI: info:10.1093/mnras/staa032v. 4924254–4267
Thompson, I. B., Udalski, A., Dotter, Aaron, Rozyczka, M., Schwarzenberg-Czerny, A., Pych, W., Beletsky, Y., Burley, G. S., Marshall, J. L., McWilliam, A., Morrell, N., Osip, D., Monson, A., Persson, S. E., Szymański, M. K., Soszyński, I., Poleski, R., Ulaczyk, K., Wyrzykowski, Ł., Kozłowski, S., Mróz, P., Pietrukowicz, P., and Skowron, J. 2020. "The Cluster AgeS Experiment (CASE) - VIII. Age and distance of the Globular Cluster 47 Tuc from the analysis of two detached eclipsing binaries." Monthly Notices of the Royal Astronomical Society 492:4254– 4267. https://doi.org/10.1093/mnras/staa032
ID: 156336
Type: article
Authors: Thompson, I. B.; Udalski, A.; Dotter, Aaron; Rozyczka, M.; Schwarzenberg-Czerny, A.; Pych, W.; Beletsky, Y.; Burley, G. S.; Marshall, J. L.; McWilliam, A.; Morrell, N.; Osip, D.; Monson, A.; Persson, S. E.; Szymański, M. K.; Soszyński, I.; Poleski, R.; Ulaczyk, K.; Wyrzykowski, Ł.; Kozłowski, S.; Mróz, P.; Pietrukowicz, P.; Skowron, J.
Abstract: We use photometric and spectroscopic observations of the eclipsing binary E32 in the globular cluster 47 Tuc to derive the masses, radii, and luminosities of the component stars. The system has an orbital period of 40.9 d, a markedly eccentric orbit with e = 0.24, and is shown to be a member of or a recent escaper from the cluster. We obtain M_p = 0.862± 0.005 M_☉, R_p = 1.183± 0.003 R_☉, L_p = 1.65± 0.05 L_☉ for the primary and M_s = 0.827± 0.005 M_☉, R_s = 1.004± 0.004 R_☉, L_s = 1.14± 0.04 L_☉ for the secondary. Based on these data and on an earlier analysis of the binary V69 in 47 Tuc, we measure the distance to the cluster from the distance moduli of the component stars, and, independently, from a colour - surface brightness calibration. We obtain 4.55 ± 0.03 and 4.50 ± 0.07 kpc, respectively - values compatible within 1 σ with recent estimates based on Gaia DR2 parallaxes. By comparing the M-R diagram of the two binaries and the colour-magnitude diagram of 47 Tuc to Dartmouth model isochrones we estimate the age of the cluster to be 12.0 ± 0.5 Gyr, and the helium abundance of the cluster to be Y ≈ 0.25.
Erratum: The Cluster Ages Experiment (CASE) - VIII. Age and distance of the Globular Cluster 47 Tuc from the analysis of two detached eclipsing binariesThompson, I. B.Udalski, A.Dotter, AaronRozyczka, M.Schwarzenberg-Czerny, A.Pych, W.Beletsky, Y.Burley, G. S.Marshall, J. L.McWilliam, A.Morrell, N.Osip, D.Monson, A.Persson, S. E.Szymański, M. K.Soszyński, I.Poleski, R.Ulaczyk, K.Wyrzykowski, Ł.Kozłowski, S.Mróz, P.Pietrukowicz, P.Skowron, J.DOI: info:10.1093/mnras/staa686v. 494846–849
Thompson, I. B., Udalski, A., Dotter, Aaron, Rozyczka, M., Schwarzenberg-Czerny, A., Pych, W., Beletsky, Y., Burley, G. S., Marshall, J. L., McWilliam, A., Morrell, N., Osip, D., Monson, A., Persson, S. E., Szymański, M. K., Soszyński, I., Poleski, R., Ulaczyk, K., Wyrzykowski, Ł., Kozłowski, S., Mróz, P., Pietrukowicz, P., and Skowron, J. 2020. "Erratum: The Cluster Ages Experiment (CASE) - VIII. Age and distance of the Globular Cluster 47 Tuc from the analysis of two detached eclipsing binaries." Monthly Notices of the Royal Astronomical Society 494:846– 849. https://doi.org/10.1093/mnras/staa686
ID: 156986
Type: article
Authors: Thompson, I. B.; Udalski, A.; Dotter, Aaron; Rozyczka, M.; Schwarzenberg-Czerny, A.; Pych, W.; Beletsky, Y.; Burley, G. S.; Marshall, J. L.; McWilliam, A.; Morrell, N.; Osip, D.; Monson, A.; Persson, S. E.; Szymański, M. K.; Soszyński, I.; Poleski, R.; Ulaczyk, K.; Wyrzykowski, Ł.; Kozłowski, S.; Mróz, P.; Pietrukowicz, P.; Skowron, J.
The GALAH survey: An abundance, age, and kinematic inventory of the solar neighbourhood made with TGASBuder, S.Lind, K.Ness, M. K.Asplund, M.Duong, L.Lin, J.Kos, J.Casagrande, L.Casey, A. R.Bland-Hawthorn, J.de Silva, G. M.D'Orazi, V.Freeman, K. C.Martell, S. L.Schlesinger, K. J.Sharma, S.Simpson, J. D.Zucker, D. B.Zwitter, T.Čotar, K.Dotter, AaronHayden, M. R.Hyde, E. A.Kafle, P. R.Lewis, G. F.Nataf, D. M.Nordlander, T.Reid, W.Rix, H. -WSkúladóttir, Á.Stello, D.Ting, Y. -STraven, G.Wyse, R. F. G.Galah CollaborationDOI: info:10.1051/0004-6361/201833218v. 624A19
Buder, S., Lind, K., Ness, M. K., Asplund, M., Duong, L., Lin, J., Kos, J., Casagrande, L., Casey, A. R., Bland-Hawthorn, J., de Silva, G. M., D'Orazi, V., Freeman, K. C., Martell, S. L., Schlesinger, K. J., Sharma, S., Simpson, J. D., Zucker, D. B., Zwitter, T., Čotar, K., Dotter, Aaron, Hayden, M. R., Hyde, E. A., Kafle, P. R., Lewis, G. F. et al. 2019. "The GALAH survey: An abundance, age, and kinematic inventory of the solar neighbourhood made with TGAS." Astronomy and Astrophysics 624:A19. https://doi.org/10.1051/0004-6361/201833218
ID: 155318
Type: article
Authors: Buder, S.; Lind, K.; Ness, M. K.; Asplund, M.; Duong, L.; Lin, J.; Kos, J.; Casagrande, L.; Casey, A. R.; Bland-Hawthorn, J.; de Silva, G. M.; D'Orazi, V.; Freeman, K. C.; Martell, S. L.; Schlesinger, K. J.; Sharma, S.; Simpson, J. D.; Zucker, D. B.; Zwitter, T.; Čotar, K.; Dotter, Aaron; Hayden, M. R.; Hyde, E. A.; Kafle, P. R.; Lewis, G. F.; Nataf, D. M.; Nordlander, T.; Reid, W.; Rix, H. -W; Skúladóttir, Á.; Stello, D.; Ting, Y. -S; Traven, G.; Wyse, R. F. G.; Galah Collaboration
Abstract: The overlap between the spectroscopic Galactic Archaeology with HERMES (GALAH) survey and Gaia provides a high-dimensional chemodynamical space of unprecedented size. We present a first analysis of a subset of this overlap, of 7066 dwarf, turn-off, and sub-giant stars. These stars have spectra from the GALAH survey and high parallax precision from the Gaia DR1 Tycho-Gaia Astrometric Solution. We investigate correlations between chemical compositions, ages, and kinematics for this sample. Stellar parameters and elemental abundances are derived from the GALAH spectra with the spectral synthesis code SPECTROSCOPY MADE EASY. We determine kinematics and dynamics, including action angles, from the Gaia astrometry and GALAH radial velocities. Stellar masses and ages are determined with Bayesian isochrone matching, using our derived stellar parameters and absolute magnitudes. We report measurements of Li, C, O, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, as well as Ba and we note that we have employed non-LTE calculations for Li, O, Al, and Fe. We show that the use of astrometric and photometric data improves the accuracy of the derived spectroscopic parameters, especially log g. Focusing our investigation on the correlations between stellar age, iron abundance [Fe/H], and mean alpha-enhancement [α/Fe] of the magnitude-selected sample, we recover the result that stars of the high-α sequence are typically older than stars in the low-α sequence, the latter spanning iron abundances of -0.7 8 Gyr) have lower angular momenta Lz than the Sun, which implies that they are on eccentric orbits and originate from the inner disc. Contrary to some previous smaller scale studies we find a continuous evolution in the high-α-sequence up to super-solar [Fe/H] rather than a gap, which has been interpreted as a separate "high-α metal-rich" population. Stars in our sample that are younger than 10 Gyr, are mainly found on the low α-sequence and show a gradient in Lz from low [Fe/H] (Lz > Lz, ☉) towards higher [Fe/H] (Lz z, ☉), which implies that the stars at the ends of this sequence are likely not originating from the close solar vicinity. The catalogue is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz- bin/qcat?J/A+A/624/A19
Hunting for brown dwarfs in the globular cluster M4: second epoch HST NIR observationsDieball, A.Bedin, L. R.Knigge, C.Geffert, M.Rich, R. M.Dotter, AaronRicher, H.Zurek, D.DOI: info:10.1093/mnras/stz996v. 4862254–2264
Dieball, A., Bedin, L. R., Knigge, C., Geffert, M., Rich, R. M., Dotter, Aaron, Richer, H., and Zurek, D. 2019. "Hunting for brown dwarfs in the globular cluster M4: second epoch HST NIR observations." Monthly Notices of the Royal Astronomical Society 486:2254– 2264. https://doi.org/10.1093/mnras/stz996
ID: 153581
Type: article
Authors: Dieball, A.; Bedin, L. R.; Knigge, C.; Geffert, M.; Rich, R. M.; Dotter, Aaron; Richer, H.; Zurek, D.
Abstract: We present an analysis of the second epoch Hubble Space TelescopeWide Field Camera 3 F110W near-infrared (NIR) imaging data of the globular cluster M 4. The new data set suggests that one of the previously suggested four brown dwarf candidates in this cluster is indeed a high- probability cluster member. The position of this object in the NIR colour-magnitude diagrams (CMDs) is in the white dwarf/brown dwarf area. The source is too faint to be a low-mass main-sequence (MS) star, but, according to theoretical considerations, also most likely somewhat too bright to be a bona-fide brown dwarf. Since we know that the source is a cluster member, we determined a new optical magnitude estimate at the position the source should have in the optical image. This new estimate places the source closer to the white dwarf sequence in the optical-NIR CMD and suggests that it might be a very cool (Teff ≤ 4500 K) white dwarf at the bottom of the white dwarf cooling sequence in M 4, or a white dwarf/brown dwarf binary. We cannot entirely exclude the possibility that the source is a very massive, bright brown dwarf, or a very low-mass MS star, however, we conclude that we still have not convincingly detected a brown dwarf in a globular cluster, but we expect to be very close to the start of the brown dwarf cooling sequence in this cluster. We also note that the MS ends at F110W ≈ 22.5 mag in the proper-motion cleaned CMDs, where completeness is still high.
Combined Effects of Rotation and Age Spreads on Extended Main-Sequence Turn OffsGossage, SethConroy, CharlieDotter, AaronCabrera-Ziri, IvanDolphin, Andrew E.Bastian, NateDalcanton, Julianne J.Goudfrooij, PaulJohnson, L. CliftonWilliams, Benjamin F.Rosenfield, PhilipKalirai, JasonFouesneau, MorganDOI: info:10.3847/1538-4357/ab5717v. 887199
Gossage, Seth, Conroy, Charlie, Dotter, Aaron, Cabrera-Ziri, Ivan, Dolphin, Andrew E., Bastian, Nate, Dalcanton, Julianne J., Goudfrooij, Paul, Johnson, L. Clifton, Williams, Benjamin F., Rosenfield, Philip, Kalirai, Jason, and Fouesneau, Morgan. 2019. "Combined Effects of Rotation and Age Spreads on Extended Main-Sequence Turn Offs." The Astrophysical Journal 887:199. https://doi.org/10.3847/1538-4357/ab5717
ID: 154536
Type: article
Authors: Gossage, Seth; Conroy, Charlie; Dotter, Aaron; Cabrera-Ziri, Ivan; Dolphin, Andrew E.; Bastian, Nate; Dalcanton, Julianne J.; Goudfrooij, Paul; Johnson, L. Clifton; Williams, Benjamin F.; Rosenfield, Philip; Kalirai, Jason; Fouesneau, Morgan
Abstract: The extended main-sequence turn offs (eMSTOs) of several young to intermediate age clusters are examined in the Magellanic Clouds and the Milky Way. We explore the effects of extended star formation (eSF) and a range of stellar rotation rates on the behavior of the color─magnitude diagram, paying particular attention to the MSTO. We create synthetic stellar populations based on MESA stellar models to simulate observed Hubble Space Telescope and Gaia star cluster data. We model the effect of rotation as a nonparametric distribution, allowing for maximum flexibility. In our models the slow rotators comprise the blueward, and fast rotators the redward portion of the eMSTO. We simulate data under three scenarios: nonrotating eSF, a range of rotation rates with a single age, and a combination of age and rotation effects. We find that two of the five clusters (the youngest and oldest) favor an age spread, but these also achieve the overall worst fits of all clusters. The other three clusters show comparable statistical evidence between rotation and an age spread. In all five cases, a rotation-rate distribution alone is capable of qualitatively matching the observed eMSTO structure. In future work, we aim to compare our predicted V\sin i with observations in order to better constrain the physics related to stellar rotation.
Helium Variation in Four Small Magellanic Cloud Globular ClustersLagioia, Edoardo P.Milone, Antonino P.Marino, Anna F.Dotter, AaronDOI: info:10.3847/1538-4357/aaf729v. 871140
Lagioia, Edoardo P., Milone, Antonino P., Marino, Anna F., and Dotter, Aaron. 2019. "Helium Variation in Four Small Magellanic Cloud Globular Clusters." The Astrophysical Journal 871:140. https://doi.org/10.3847/1538-4357/aaf729
ID: 155444
Type: article
Authors: Lagioia, Edoardo P.; Milone, Antonino P.; Marino, Anna F.; Dotter, Aaron
Abstract: The multiple stellar populations (MPs) of the ∼11-13 Gyr old globular clusters (GCs) in our Galaxy are characterized by the different content of several light elements. These elements describe well-defined patterns like the C-N and the Na-O anticorrelations and the He-N and Na-N correlations. The discovery of MPs in Magellanic Cloud GCs opened up new paths for the investigation of chemical anomalies in clusters with different ages and physical properties. In this context, we used Hubble Space Telescope photometry to investigate the MPs and constrain their chemical composition of four ∼6-11 Gyr extragalactic GCs, namely NGC 121, NGC 339, NGC 416, and Lindsay 1 in the Small Magellanic Cloud. The comparison of the stellar colors with synthetic spectra suggests that the second-population stars of NGC 121, NGC 339, and NGC 416 are slightly enhanced in helium by δ Y=0.009+/- 0.006,0.007+/- 0.004 and 0.010 ± 0.003, respectively, with respect to the first population, while we find no significant helium variation in Lindsay 1 (δ Y=0.000+/- 0.004). Moreover, the second-population stars of all the clusters are, on average, enhanced in nitrogen and depleted in carbon and oxygen, in close analogy with what we observe in Galactic GCs.
Chemical (in)homogeneity and atomic diffusion in the open cluster M 67Liu, F.Asplund, M.Yong, D.Feltzing, S.Dotter, AaronMeléndez, J.Ramírez, I.DOI: info:10.1051/0004-6361/201935306v. 627A117
Liu, F., Asplund, M., Yong, D., Feltzing, S., Dotter, Aaron, Meléndez, J., and Ramírez, I. 2019. "Chemical (in)homogeneity and atomic diffusion in the open cluster M 67." Astronomy and Astrophysics 627:A117. https://doi.org/10.1051/0004-6361/201935306
ID: 155126
Type: article
Authors: Liu, F.; Asplund, M.; Yong, D.; Feltzing, S.; Dotter, Aaron; Meléndez, J.; Ramírez, I.
Abstract: Context. The benchmark open cluster M 67 is known to have solar metallicity and an age similar to that of the Sun. It thus provides us with a great opportunity to study the properties of solar twins, as well as the evolution of Sun-like stars. Aims: Previous spectroscopic studies of M 67 reported possible subtle changes in stellar surface abundances throughout the stellar evolutionary phase, namely the effect of atomic diffusion. In this study we attempt to confirm and quantify more precisely the effect of atomic diffusion, and to explore the level of chemical (in)homogeneity in M 67. Methods: We presented a strictly line-by-line differential chemical abundance analysis of two groups of stars in M 67: three turn-off stars and three subgiants. Stellar atmospheric parameters and elemental abundances were obtained with very high precision using the Keck/HIRES spectra. Results: The subgiants in our sample show negligible abundance variations (≤0.02 dex), which implies that M 67 was born chemically homogeneous. We note that there is a significant abundance difference ( 0.1-0.2 dex) between subgiants and turn-off stars, which can be interpreted as the signature of atomic diffusion. Qualitatively stellar models with diffusion agree with the observed abundance results. Some turn-off stars do not follow the general pattern, which suggests that in some cases diffusion can be inhibited, or they might have undergone some sort of mixing event related to planets. Conclusions: Our results pose additional challenges for chemical tagging when using turn-off stars. In particular, the effects of atomic diffusion, which could be as large as 0.1-0.2 dex, must be taken into account in order for chemical tagging to be successfully applied. Table A.1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz- bin/qcat?J/A+A/627/A117The data presented here were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation.
Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy ConservationPaxton, BillSmolec, R.Schwab, JosiahGautschy, A.Bildsten, LarsCantiello, MatteoDotter, AaronFarmer, R.Goldberg, Jared A.Jermyn, Adam S.Kanbur, S. M.Marchant, PabloThoul, AnneTownsend, Richard H. D.Wolf, William M.Zhang, MichaelTimmes, F. X.DOI: info:10.3847/1538-4365/ab2241v. 24310
Paxton, Bill, Smolec, R., Schwab, Josiah, Gautschy, A., Bildsten, Lars, Cantiello, Matteo, Dotter, Aaron, Farmer, R., Goldberg, Jared A., Jermyn, Adam S., Kanbur, S. M., Marchant, Pablo, Thoul, Anne, Townsend, Richard H. D., Wolf, William M., Zhang, Michael, and Timmes, F. X. 2019. "Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation." The Astrophysical Journal Supplement Series 243:10. https://doi.org/10.3847/1538-4365/ab2241
ID: 155125
Type: article
Authors: Paxton, Bill; Smolec, R.; Schwab, Josiah; Gautschy, A.; Bildsten, Lars; Cantiello, Matteo; Dotter, Aaron; Farmer, R.; Goldberg, Jared A.; Jermyn, Adam S.; Kanbur, S. M.; Marchant, Pablo; Thoul, Anne; Townsend, Richard H. D.; Wolf, William M.; Zhang, Michael; Timmes, F. X.
Abstract: We update the capabilities of the open-knowledge software instrument Modules for Experiments in Stellar Astrophysics (MESA). RSP is a new functionality in MESAstar that models the nonlinear radial stellar pulsations that characterize RR Lyrae, Cepheids, and other classes of variable stars. We significantly enhance numerical energy conservation capabilities, including during mass changes. For example, this enables calculations through the He flash that conserve energy to better than 0.001%. To improve the modeling of rotating stars in MESA, we introduce a new approach to modifying the pressure and temperature equations of stellar structure, as well as a formulation of the projection effects of gravity darkening. A new scheme for tracking convective boundaries yields reliable values of the convective core mass and allows the natural emergence of adiabatic semiconvection regions during both core hydrogen- and helium-burning phases. We quantify the parallel performance of MESA on current-generation multicore architectures and demonstrate improvements in the computational efficiency of radiative levitation. We report updates to the equation of state and nuclear reaction physics modules. We briefly discuss the current treatment of fallback in core-collapse supernova models and the thermodynamic evolution of supernova explosions. We close by discussing the new MESA Testhub software infrastructure to enhance source code development.
They Might Be Giants: An Efficient Color-based Selection of Red Giant StarsConroy, CharlieBonaca, AnaNaidu, Rohan P.Eisenstein, Daniel J.Johnson, Benjamin D.Dotter, AaronFinkbeiner, Douglas P.DOI: info:10.3847/2041-8213/aacdf1v. 861L16
Conroy, Charlie, Bonaca, Ana, Naidu, Rohan P., Eisenstein, Daniel J., Johnson, Benjamin D., Dotter, Aaron, and Finkbeiner, Douglas P. 2018. "They Might Be Giants: An Efficient Color-based Selection of Red Giant Stars." Astrophysical Journal Letters 861:L16. https://doi.org/10.3847/2041-8213/aacdf1
ID: 147906
Type: article
Authors: Conroy, Charlie; Bonaca, Ana; Naidu, Rohan P.; Eisenstein, Daniel J.; Johnson, Benjamin D.; Dotter, Aaron; Finkbeiner, Douglas P.
Abstract: We present a color-based method for identifying red giants based on the Pan-STARRS grz and WISE W1 and W2 photometry. We utilize a subsample of bright stars with precise parallaxes from Gaia's second data release (DR2) to verify that the color-based selection reliably separates dwarfs from giants. The selection is conservative in the sense that contamination is small (≈30%) but not all giants are included (the selection primarily identifies K giants). The color-based selection can be applied to stars brighter than W1 ≈ 16, more than two magnitudes fainter than techniques relying on shallower 2MASS photometry. Many streams and clouds are visible in the resulting sky maps, especially when binned by Gaia DR2 proper motions, including the Sagittarius stream, the Hercules--Aquila Cloud, the Eastern Banded Structure, Monoceros, and the Virgo Overdensity. In addition to the characterization of new and known stellar streams, we expect that this method for selecting red giants will enable detailed analysis of the diffuse stellar halo to distances exceeding 100 kpc.
Stellar ages and masses in the solar neighbourhood: Bayesian analysis using spectroscopy and Gaia DR1 parallaxesLin, JaneDotter, AaronTing, Yuan-SenAsplund, MartinDOI: info:10.1093/mnras/sty709v. 4772966–2975
Lin, Jane, Dotter, Aaron, Ting, Yuan-Sen, and Asplund, Martin. 2018. "Stellar ages and masses in the solar neighbourhood: Bayesian analysis using spectroscopy and Gaia DR1 parallaxes." Monthly Notices of the Royal Astronomical Society 477:2966– 2975. https://doi.org/10.1093/mnras/sty709
ID: 147895
Type: article
Authors: Lin, Jane; Dotter, Aaron; Ting, Yuan-Sen; Asplund, Martin
Abstract: We present a Bayesian implementation of isochrone fitting in deriving stellar ages and masses, incorporating absolute K magnitude (M_K) derived from 2MASS photometry and Gaia DR1 parallax and differentiation between initial bulk metallicity and present-day surface metallicity, with allowance for incorporating further constraints (e.g. asteroseismology) when available. As a test, we re-computed stellar ages and masses of &tilde;4000 stars in the solar neighbourhood from six well-studied literature samples using both Hipparcos and TGAS parallaxes. Our ages are found to be compatible with literature values but with reduced uncertainties in general. The inclusion of parallax-based M_K serves as an additional constraint on the derived quantities, especially when systematic errors in stellar parameters are underestimated. We reconstructed the age-metallicity relationship in the solar neighbourhood by re-analysing the Geneva-Copenhagen Survey with the inclusion of TGAS-parallaxes and initial bulk metallicity sampling. We found a flat trend for disc stars with ages <11 Gyr but with smaller scatter at all ages compared to literature.
Different Stellar Rotations in the Two Main Sequences of the Young Globular Cluster NGC 1818: The First Direct Spectroscopic EvidenceMarino, A. F.Przybilla, N.Milone, A. P.Da Costa, G.D'Antona, F.Dotter, AaronDupree, A.DOI: info:10.3847/1538-3881/aad3cdv. 156116
Marino, A. F., Przybilla, N., Milone, A. P., Da Costa, G., D'Antona, F., Dotter, Aaron, and Dupree, A. 2018. "Different Stellar Rotations in the Two Main Sequences of the Young Globular Cluster NGC 1818: The First Direct Spectroscopic Evidence." The Astronomical Journal 156:116. https://doi.org/10.3847/1538-3881/aad3cd
ID: 149184
Type: article
Authors: Marino, A. F.; Przybilla, N.; Milone, A. P.; Da Costa, G.; D'Antona, F.; Dotter, Aaron; Dupree, A.
Abstract: We present a spectroscopic analysis of main sequence (MS) stars in the young globular cluster NGC 1818 (age ∼40 Myr) in the Large Magellanic Cloud. Our photometric survey of Magellanic Clouds clusters has revealed that NGC 1818, similar to other young objects with ages ≲600 Myr, displays not only an extended MS turnoff (eMSTO), as observed in intermediate-age clusters (age ∼1–2 Gyr), but also a split MS. The most straightforward interpretation of the double MS is the presence of two stellar populations: a sequence of slowly rotating stars lying on the blue-MS (bMS) and a sequence of fast rotators, with rotation close to the breaking speed, defining a red-MS (rMS). We report the first direct spectroscopic measurements of projected rotational velocities v\sin i for the double MS, eMSTO, and Be stars of a young cluster. The analysis of line profiles includes non-local thermodynamic equilibrium effects, required for correctly deriving v\sin i values. Our results suggest that: (i) the mean rotation for bMS and rMS stars is v\sin i =71 ± 10 km s‑1 (σ = 37 km s‑1) and v\sin i = 202 ± 23 km s‑1 (σ = 91 km s‑1), respectively; (ii) eMSTO stars have different v\sin i, which are generally lower than those inferred for rMS stars, and (iii) as expected, Be stars display the highest v\sin i values. This analysis supports the idea that distinct rotational velocities play an important role in the appearance of multiple stellar populations in the color–magnitude diagrams of young clusters, and poses new constraints on the current scenarios. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 0100.D-0520(A), and observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.
NGC 1866: First Spectroscopic Detection of Fast-rotating Stars in a Young LMC ClusterDupree, A. K.Dotter, AaronJohnson, C. I.Marino, A. F.Milone, A. P.Bailey, J. I., IIICrane, J. D.Mateo, M.Olszewski, E. W.DOI: info:10.3847/2041-8213/aa85ddv. 846L1
Dupree, A. K., Dotter, Aaron, Johnson, C. I., Marino, A. F., Milone, A. P., Bailey, J. I., III, Crane, J. D., Mateo, M., and Olszewski, E. W. 2017. "NGC 1866: First Spectroscopic Detection of Fast-rotating Stars in a Young LMC Cluster." Astrophysical Journal Letters 846:L1. https://doi.org/10.3847/2041-8213/aa85dd
ID: 144711
Type: article
Authors: Dupree, A. K.; Dotter, Aaron; Johnson, C. I.; Marino, A. F.; Milone, A. P.; Bailey, J. I., III; Crane, J. D.; Mateo, M.; Olszewski, E. W.
Abstract: High-resolution spectroscopic observations were taken of 29 extended main-sequence turnoff (eMSTO) stars in the young (˜200 Myr) Large Magellanic Cloud (LMC) cluster, NGC 1866, using the Michigan/Magellan Fiber System and MSpec spectrograph on the Magellan-Clay 6.5 m telescope. These spectra reveal the first direct detection of rapidly rotating stars whose presence has only been inferred from photometric studies. The eMSTO stars exhibit Hα emission (indicative of Be-star decretion disks), others have shallow broad Hα absorption (consistent with rotation ≳150 km s-1), or deep Hα core absorption signaling lower rotation velocities (≲150 km s-1). The spectra appear consistent with two populations of stars-one rapidly rotating, and the other, younger and slowly rotating.
Capella (a Aurigae) Revisited: New Binary Orbit, Physical Properties, and Evolutionary StateTorres, GuillermoClaret, AntonioPavlovski, KrešimirDotter, AaronDOI: info:10.1088/0004-637X/807/1/26v. 80726
Torres, Guillermo, Claret, Antonio, Pavlovski, Krešimir, and Dotter, Aaron. 2015. "Capella (a Aurigae) Revisited: New Binary Orbit, Physical Properties, and Evolutionary State." The Astrophysical Journal 807:26. https://doi.org/10.1088/0004-637X/807/1/26
ID: 136984
Type: article
Authors: Torres, Guillermo; Claret, Antonio; Pavlovski, Krešimir; Dotter, Aaron
Abstract: Knowledge of the chemical composition and absolute masses of Capella are key to understanding the evolutionary state of this benchmark binary system comprising two giant stars. Previous efforts, including our own 2009 study, have largely failed to reach an acceptable agreement between the observations and current stellar evolution models, preventing us from assessing the status of the primary. Here we report a revision of the physical properties of the components incorporating recently published high-precision radial velocity measurements, and a new detailed chemical analysis providing abundances for more than 20 elements in both stars. We obtain highly precise (~0.3%) masses of 2.5687 ± 0.0074 {M}? and 2.4828 ± 0.0067 {M}? , radii of 11.98 ± 0.57 {R}? and 8.83 ± 0.33 {R}? , effective temperatures of 4970 ± 50 and 5730 ± 60 K, and independently measured luminosities based on the orbital parallax (78.7 ± 4.2 {L}? and 72.7 ± 3.6 {L}? ). We find an excellent match to stellar evolution models at the measured composition of [{Fe}/{{H}}]=-0.04+/- 0.06. Three different sets of models place the primary star firmly at the end of the core helium-burning phase (clump), while the secondary is known to be evolving rapidly across the Hertzprung gap. The measured lithium abundance, the C/N ratio, and the 12C/13C isotopic carbon abundance ratio, which change rapidly in the giant phase, are broadly in agreement with expectations from models. Predictions from tidal theory for the spin rates, spin–orbit alignment, and other properties do not fare as well, requiring a 40-fold increase in the efficiency of the dissipation mechanisms in order to match the observations.