1,511 results on '"Ramírez, I."'
Search Results
2. Palliative care management in patients with Parkinson’s disease and other movement disorders in Spain. National survey of neurologists
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Álvarez Saúco, M., García- Ramos, R., Legarda Ramírez, I., Carrillo García, F., Fernández Bueno, J., Martí Martínez, S., González García, B., Moya-Martínez, A., and Santos-García, D.
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- 2024
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3. Manejo de la atención paliativa de los pacientes con enfermedad de Parkinson y otros trastornos del movimiento en España. Encuesta Nacional a neurólogos
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Álvarez Saúco, M., García- Ramos, R., Legarda Ramírez, I., Carrillo García, F., Fernández Bueno, J., Martí Martínez, S., González García, B., Moya-Martínez, A., and Santos-García, D.
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- 2024
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4. Acute and chronic mammary periprosthetic histological changes of the muscle
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Cámara-Pérez, J., Jimena, I., Rodríguez-Cano, M.A., Sanz-Zorrilla, A., Osuna-Soto, J., Sánchez-Ramírez, I., Sánchez-Medianero, T., Gálvez-Medina, M.J., Ortega-Salas, R., and Leiva-Cepas, F.
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- 2024
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5. Detailed chemical compositions of planet hosting stars: I. Exploration of possible planet signatures
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Liu, F., Yong, D., Asplund, M., Wang, H. S., Spina, L., Acuna, L., Melendez, J., and Ramirez, I.
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Astrophysics - Solar and Stellar Astrophysics ,Astrophysics - Earth and Planetary Astrophysics ,Astrophysics - Astrophysics of Galaxies - Abstract
We present a line-by-line differential analysis of a sample of 16 planet hosting stars and 68 comparison stars using high resolution, high signal-to-noise ratio spectra gathered using Keck. We obtained accurate stellar parameters and high-precision relative chemical abundances with average uncertainties in \teff, \logg, [Fe/H] and [X/H] of 15 K, 0.034 [cgs], 0.012 dex and 0.025 dex, respectively. For each planet host, we identify a set of comparison stars and examine the abundance differences (corrected for Galactic chemical evolution effect) as a function of the dust condensation temperature, \tcond, of the individual elements. While we confirm that the Sun exhibits a negative trend between abundance and \tcond, we also confirm that the remaining planet hosts exhibit a variety of abundance $-$ \tcond\ trends with no clear dependence upon age, metallicity or \teff. The diversity in the chemical compositions of planet hosting stars relative to their comparison stars could reflect the range of possible planet-induced effects present in these planet hosts, from the sequestration of rocky material (refractory poor), to the possible ingestion of planets (refractory rich). Other possible explanations include differences in the timescale, efficiency and degree of planet formation or inhomogeneous chemical evolution. Although we do not find an unambiguous chemical signature of planet formation among our sample, the high-precision chemical abundances of the host stars are essential for constraining the composition and structure of their exoplanets., Comment: 14 pages, 10 figures, accepted for publication in MNRAS
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- 2020
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6. Gemini-GRACES high-quality spectra of Kepler evolved stars with transiting planets I. Detailed characterization of multi-planet systems Kepler-278 and Kepler-391
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Jofré, E., Almenara, J. M., Petrucci, R., Díaz, R. F., Chew, Y. Gómez Maqueo, Martioli, E., Ramírez, I., García, L., Saffe, C., Canul, E. F., Buccino, A., Gómez, M., and Hilario, E. Moreno
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Astrophysics - Earth and Planetary Astrophysics ,Astrophysics - Solar and Stellar Astrophysics - Abstract
(abridged) Kepler-278 and Kepler-391 are two of the three evolved stars known to date on the RGB to host multiple short-period transiting planets. Moreover, these planets are among the smallest discovered around RGB stars. Here we present a detailed stellar and planetary characterization of these remarkable systems. Based on high-quality spectra from Gemini-GRACES for Kepler-278 and Kepler-391, we obtained refined stellar parameters and precise chemical abundances for 25 elements. Also, combining our new stellar parameters with a photodynamical analysis of the Kepler light curves, we determined accurate planetary properties of both systems. The precise spectroscopic parameters of Kepler-278 and Kepler-391, along with their high $^{12}\mathrm{C}/^{13}\mathrm{C}$ ratios, show that both stars are just starting their ascent on the RGB. The planets Kepler-278b, Kepler-278c, and Kepler-391c are warm sub-Neptunes, whilst Kepler-391b is a hot sub-Neptune that falls in the hot super-Earth desert and, therefore, it might be undergoing photoevaporation of its outer envelope. The high-precision obtained in the transit times allowed us not only to confirm Kepler-278c's TTV signal, but also to find evidence of a previously undetected TTV signal for the inner planet Kepler-278b. From the presence of gravitational interaction between these bodies we constrain, for the first time, the mass of Kepler-278b ($M_{\mathrm{p}}$ = 56 $\substack{+37\\-13}$ $M_{\mathrm{\oplus}}$) and Kepler-278c ($M_{\mathrm{p}}$ = 35 $\substack{+9.9\\ -21} $ $M_{\mathrm{\oplus}}$). Finally, our photodynamical analysis also shows that the orbits of both planets around Kepler-278 are highly eccentric ($e \sim$ 0.7) and, surprisingly, coplanar. Further observations of this system are needed to confirm the eccentricity values presented here., Comment: Accepted for publication in A&A. 33 pages, 22 figures, 4 tables -v2: Some language editing included and typos corrected
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- 2019
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7. The chemical composition of HIP34407/HIP34426 and other twin-star comoving pairs
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Ramirez, I., Khanal, S., Lichon, S. J., Chaname, J., Endl, M., Melendez, J., and Lambert, D. L.
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Astrophysics - Solar and Stellar Astrophysics - Abstract
We conducted a high-precision elemental abundance analysis of the twin-star comoving pair HIP34407/HIP34426. With mean error of 0.013 dex in the differential abundances (D[X/H]), a significant difference was found: HIP34407 is more metal-rich than HIP34426. The elemental abundance differences correlate strongly with condensation temperature, with the lowest for the volatile elements like carbon around 0.05+/-0.02 dex, and the highest up to about 0.22+/-0.01 dex for the most refractory elements like aluminum. Dissimilar chemical composition for stars in twin-star comoving pairs are not uncommon, thus we compile previously-published results like ours and look for correlations between abundance differences and stellar parameters, finding no significant trends with average effective temperature, surface gravity, iron abundance, or their differences. Instead, we found a weak correlation between the absolute value of abundance difference and the projected distance between the stars in each pair that appears to be more important for elements which have a low absolute abundance. If confirmed, this correlation could be an important observational constraint for binary star system formation scenarios., Comment: MNRAS, in press
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- 2019
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8. Bimetallic systems of ZnO/Al/Ag applied on cell PEC and photocatalytic system
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Ortiz Rabell, G., Juárez-Ramírez, I., and Alfaro Cruz, M.R.
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- 2023
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9. The Li-age correlation: the Sun is unusually Li deficient for its age
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Carlos, M., Melendez, J., Spina, L., Santos, L. A. dos, Bedell, M., Ramirez, I., Asplund, M., Bean, J. L., Yong, D., Galarza, J. Yana, and Alves-Brito, A.
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Astrophysics - Solar and Stellar Astrophysics - Abstract
The present work aims to examine in detail the depletion of lithium in solar twins to better constrain stellar evolution models and investigate its possible connection with exoplanets. We employ spectral synthesis in the region of the asymmetric 6707.75 \AA Li I line for a sample of 77 stars plus the Sun. As in previous works based on a smaller sample of solar twins, we find a strong correlation between Li depletion and stellar age. In addition, for the first time we show that the Sun has the lowest Li abundance in comparison with solar twins at similar age (4.6 $\pm$ 0.5 Gyr). We compare the lithium content with the condensation temperature slope for a sub-sample of the best solar twins and determine that the most lithium depleted stars also have fewer refractory elements. We speculate whether the low lithium content in the Sun might be related to the particular configuration of our Solar system., Comment: Accepted for publication at MNRAS, 9 pages, 6 figures and 1 table
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- 2019
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10. Chemical (in)homogeneity and atomic diffusion in the open cluster M67
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Liu, F., Asplund, M., Yong, D., Feltzing, S., Dotter, A., Meléndez, J., and Ramírez, I.
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Astrophysics - Solar and Stellar Astrophysics - Abstract
Context. The benchmark open cluster M67 is known to have solar metallicity and similar age as the Sun. It thus provides us a great opportunity to study the properties of solar twins, as well as the evolution of Sun-like stars. Aims. Previous spectroscopic studies reported to detect possible subtle changes in stellar surface abundances throughout the stellar evolutionary phase, namely the effect of atomic diffusion, in M67. In this study we attempt to confirm and quantify more precisely the effect of atomic diffusion, as well as to explore the level of chemical (in)homogeneity in M67. Methods. We presented a strictly line-by-line differential chemical abundance analysis of two groups of stars in M67: three turn-off stars and three sub-giants. Stellar atmospheric parameters and elemental abundances were obtained with very high precision using the Keck/HIRES spectra. Results. The sub-giants in our sample show negligible abundance variations ($\le$ 0.02 dex), which implies that M67 was born chemically homogeneous. We note there is a significant abundance difference ($\sim$ 0.1 - 0.2 dex) between sub-giants 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 suffered 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., Comment: 19 pages, 21 figures; submitted to A&A on February, 2019, accepted for publication in A&A on June, 2019
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- 2019
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11. Photochemistry of ZnO/GeO2 film for H2 production
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Ortiz Rabell, G., Alfaro Cruz, M.R., and Juárez-Ramírez, I.
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- 2022
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12. Detailed chemical compositions of the wide binary HD 80606/80607: revised stellar properties and constraints on planet formation
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Liu, F., Yong, D., Asplund, M., Feltzing, S., Mustill, A. J., Meléndez, J., Ramírez, I., and Lin, J.
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Astrophysics - Solar and Stellar Astrophysics ,Astrophysics - Earth and Planetary Astrophysics - Abstract
Differences in the elemental abundances of planet hosting stars in binary systems can give important clues and constraints about planet formation and evolution. In this study we performed a high-precision, differential elemental abundance analysis of a wide binary system, HD 80606/80607, based on high-resolution, high signal-to-noise ratio Keck/HIRES spectra. HD 80606 is known to host a four Jupiter mass giant planet while no planet has yet been detected around HD 80607. We determined stellar parameters as well as abundances for 23 elements for these two stars with extremely high precision. Our main results are: (i) we confirmed that the two components share very similar chemical compositions, but HD 80606 is marginally more metal-rich than HD 80607 with an average difference of +0.013 $\pm$ 0.002 dex ($\sigma$ = 0.009 dex) and (ii) there is no obvious trend between abundance differences and condensation temperature. Assuming this binary formed from material with the same chemical composition, it is difficult to understand how giant planet formation could produce the present-day photospheric abundances of the elements we measure. We can not exclude the possibility that HD 80606 might have accreted about 2.5 to 5 $M_{\rm Earth}$ material onto its surface, possibly from a planet destabilised by the known highly-eccentric giant., Comment: 11 pages, 9 figues, accepted for publication in A&A
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- 2018
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13. iota Horologii is unlikely to be an evaporated Hyades star
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Ramirez, I., Yong, D., Gutierrez, E., Endl, M., Lambert, D. L., and Nascimento Jr, J. -D. Do
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Astrophysics - Solar and Stellar Astrophysics - Abstract
We present a high-precision chemical analysis of iota Horologii, a planet-host field star thought to have formed in the Hyades. Elements with atomic number 6<=Z<=30 have abundances that are in excellent agreement with those of the cluster within the +/-0.01 dex (or ~2%) precision errors. Heavier elements show a range of abundances such that about half of the Z>30 species analyzed are consistent with those of the Hyades, while the other half are marginally enhanced by 0.03+/-0.01 dex (~7+/-2%). The lithium abundance, A(Li), is very low compared to the well-defined A(Li)-Teff relation of the cluster. For its Teff, iota Horologii's lithium content is about half the Hyades'. Attributing the enhanced lithium depletion to the planet would require a peculiar rotation rate, which we are unable to confirm. Our analysis of the star's chromospheric activity suggests Prot=5d, which is significantly shorter than previously reported. Models of Galactic orbits place iota Horologii hundreds of parsecs away from the Hyades cluster at formation. Thus, we find the claim of a shared birthplace very difficult to justify., Comment: ApJ, in press
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- 2017
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14. Into the Woods: An Epistemography of Climate Change
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Ramírez-i-Ollé, Meritxell, author and Ramírez-i-Ollé, Meritxell
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- 2020
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15. Photoelectrochemical (PEC) analysis of ZnO/Al photoelectrodes and its photocatalytic activity for hydrogen production
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Rabell, G. Ortiz, Alfaro Cruz, M.R., and Juárez-Ramírez, I.
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- 2022
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16. Machine Protection, Interlocks and Availability
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Apollonio, A., Baer, T., Dahlerup-Petersen, K., Denz, R., Ramirez, I. Romera, Schmidt, R., Siemko, A., Wenninger, J., Wollmann, D., and Zerlauth, M.
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Physics - Accelerator Physics - Abstract
Chapter 7 in High-Luminosity Large Hadron Collider (HL-LHC) : Preliminary Design Report. The Large Hadron Collider (LHC) is one of the largest scientific instruments ever built. Since opening up a new energy frontier for exploration in 2010, it has gathered a global user community of about 7,000 scientists working in fundamental particle physics and the physics of hadronic matter at extreme temperature and density. To sustain and extend its discovery potential, the LHC will need a major upgrade in the 2020s. This will increase its luminosity (rate of collisions) by a factor of five beyond the original design value and the integrated luminosity (total collisions created) by a factor ten. The LHC is already a highly complex and exquisitely optimised machine so this upgrade must be carefully conceived and will require about ten years to implement. The new configuration, known as High Luminosity LHC (HL-LHC), will rely on a number of key innovations that push accelerator technology beyond its present limits. Among these are cutting-edge 11-12 tesla superconducting magnets, compact superconducting cavities for beam rotation with ultra-precise phase control, new technology and physical processes for beam collimation and 300 metre-long high-power superconducting links with negligible energy dissipation. The present document describes the technologies and components that will be used to realise the project and is intended to serve as the basis for the detailed engineering design of HL-LHC., Comment: 10 pages, chapter 7 in High-Luminosity Large Hadron Collider (HL-LHC) : Preliminary Design Report
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- 2017
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17. Seabird bycatch in European waters.
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Ramírez, I., Mitchell, D., Vulcano, A., Rouxel, Y., Marchowski, D., Almeida, A., Arcos, J. M., Cortes, V., Lange, G., Morkūnas, J., Oliveira, N., and Paiva, V. H.
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BYCATCHES , *NUMBERS of species , *MIGRATORY animals , *ACQUISITION of data , *FISHERIES - Abstract
The incidental capture (bycatch) of seabirds is a global conservation issue and a top threat to European species that demands urgent conservation and management action. Here, we present the first European review of seabird bycatch data, considering all fishing gears and data collection methods available in the region. We calculate seabird bycatch numbers per species, family, country and European marine region and assess the reliability of the data available. The cumulative bycatch estimate extracted from this review suggests that about 195,000 seabirds (ranging from around 130,000 to 380,000) are bycaught in European waters annually. The most affected seabird species is the Common Guillemot Uria aalge with over 31,000 birds killed per year. The marine region with the highest bycatch estimate is the Northeast Atlantic (over 115,000 seabirds year−1). Gillnet fisheries are responsible for the highest bycatch levels, with over 95,000 seabirds year−1, followed by longline fisheries. The families most affected by bycatch are Anatidae and Alcidae. These numbers are likely an underestimation since we were unable to find bycatch estimates, or to extrapolate estimates from available bycatch data for 12 (out of 34) European coastal states. Our assessment also identified significant data gaps in key areas such as Gran Sol (in the north‐east Atlantic), the central and Eastern Mediterranean and the Black Sea. Combining systematic data collection with immediate implementation of mitigation measures will be crucial to fill in knowledge gaps, reduce current mortality levels and meet international conservation commitments such as those of the European Union and the Convention on Migratory Species. [ABSTRACT FROM AUTHOR]
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- 2024
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18. Host‐plant sex and phenology of Buddleja cordata Kunth interact to influence arthropod communities.
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González‐Ramírez, I., López‐Gómez, V., Cano‐Santana, Z., Romero Pérez, A., and Hernández Cumplido, J.
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DIMORPHISM in plants , *SOCIAL influence , *SEXUAL dimorphism , *PLANT phenology , *PHENOLOGY , *PLANT variation - Abstract
Intraspecific variation in plants is expected to have profound impacts on the arthropod communities associated with them. Because sexual dimorphism in plants is expected to provide consistent variation among individuals of the same species, researchers have often studied the effect it has on associated arthropods. Nevertheless, most studies have focused on the effect of sexual dimorphism in a single or a few herbivores, thus overlooking the potential effects on the whole arthropod community. Our main objective was to evaluate effects of Buddleja cordata's plant‐sex on its associated arthropod community. We surveyed 13 pairs of male and female plants every 2 months during a year (June 2010 to April 2011). Every sampling date, we measured plant traits (water content and leaf thickness), herbivory, and the arthropod community. We did not find differences in herbivory between plant sex or through time. However, we found differences in water content through time, with leaf water‐content matching the environmental seasonality. For arthropod richness, we found 68 morphospecies associated with female and 72 with male plants, from which 53 were shared by both sexes. We did not observe differences in morphospecies richness; however, we found sex‐associated differences in the diversity of all species and differences on the diversity of the most abundant species with an interesting temporal component. During peak flowering season, male plants showed higher values on both parameters, but during the peak fructification season female plants showed the higher values on both diversity parameters. Our research exemplifies the interaction between plant‐phenology and plant‐sex as drivers of arthropod communities' diversity, even when plant sexual‐dimorphism is inconspicuous, and highlighting the importance of accounting for seasonal variation. We stress the need of conducting more studies that test this time‐dependent framework in other dioecious systems, as it has the potential to reconcile previous contrasting observations reported in the literature. [ABSTRACT FROM AUTHOR]
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- 2024
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19. How much can we trust high-resolution spectroscopic stellar chemical abundances?
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Blanco-Cuaresma, S., Nordlander, T., Heiter, U., Jofré, P., Masseron, T., Casamiquela, L., Tabernero, H. M., Bhat, S. S., Casey, A. R., Meléndez, J., and Ramírez, I.
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Astrophysics - Solar and Stellar Astrophysics ,Astrophysics - Instrumentation and Methods for Astrophysics - Abstract
To study stellar populations, it is common to combine chemical abundances from different spectroscopic surveys/studies where different setups were used. These inhomogeneities can lead us to inaccurate scientific conclusions. In this work, we studied one aspect of the problem: When deriving chemical abundances from high-resolution stellar spectra, what differences originate from the use of different radiative transfer codes?, Comment: To appear in the Highlights on Spanish Astrophysics IX, Proceedings of the XII Scientific Meeting of the Spanish Astronomical Society
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- 2016
20. How much can we trust high-resolution spectroscopic stellar atmospheric parameters?
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Blanco-Cuaresma, S., Nordlander, T., Heiter, U., Jofré, P., Masseron, T., Casamiquela, L., Tabernero, H. M., Bhat, S. S., Casey, A. R., Meléndez, J., and Ramírez, I.
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Astrophysics - Solar and Stellar Astrophysics ,Astrophysics - Instrumentation and Methods for Astrophysics - Abstract
The determination of atmospheric parameters depends on the use of radiative transfer codes (among other elements such as model atmospheres) to compute synthetic spectra and/or derive abundances from equivalent widths. However, it is common to mix results from different surveys/studies where different setups were used to derive the parameters. These inhomogeneities can lead us to inaccurate conclusions. In this work, we studied one aspect of the problem: When deriving atmospheric parameters from high-resolution stellar spectra, what differences originate from the use of different radiative transfer codes?, Comment: To appear in the 19th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun proceeding
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- 2016
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21. Catalytic hydrothermal liquefaction of microalgae cultivated in wastewater: Influence of ozone-air flotation on products, energy balance and carbon footprint
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Nava-Bravo, I., Velasquez-Orta, S.B., Monje-Ramírez, I., Güereca, L.P., Harvey, A.P., Cuevas-García, R., Yáñez-Noguez, I., and Orta-Ledesma, M.T.
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- 2021
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22. First insight into plastics ingestion by fish in the Gulf of California, Mexico
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Salazar-Pérez, C., Amezcua, F., Rosales-Valencia, A., Green, L., Pollorena-Melendrez, J.E., Sarmiento-Martínez, M.A., Tomita Ramírez, I., Gil-Manrique, B.D., Hernandez-Lozano, M.Y., Muro-Torres, V.M., Green-Ruiz, C., Piñon-Colin, T.D.J., Wakida, F.T., and Barletta, M.
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- 2021
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23. The chemical compositions of solar twins in the open cluster M67
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Liu, F., Asplund, M., Yong, D., Melendez, J., Ramirez, I., Karakas, A. I., Carlos, M., and Marino, A. F.
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Astrophysics - Solar and Stellar Astrophysics - Abstract
Stars in open clusters are expected to share an identical abundance pattern. Establishing the level of chemical homogeneity in a given open cluster deserves further study as it is the basis of the concept of chemical tagging to unravel the history of the Milky Way. M67 is particularly interesting given its solar metallicity and age as well as being a dense cluster environment. We conducted a strictly line-by-line differential chemical abundance analysis of two solar twins in M67: M67-1194 and M67-1315. Stellar atmospheric parameters and elemental abundances were obtained with high precision using Keck/HIRES spectra. M67-1194 is essentially identical to the Sun in terms of its stellar parameters. M67-1315 is warmer than M67-1194 by ~ 150 K as well as slightly more metal-poor than M67-1194 by ~ 0.05 dex. M67-1194 is also found to have identical chemical composition to the Sun, confirming its solar twin nature. The abundance ratios [X/Fe] of M67-1315 are similar to the solar abundances for elements with atomic number Z <= 30, while most neutron-capture elements are enriched by ~ 0.05 dex, which might be attributed to enrichment from a mixture of AGB ejecta and r-process material. The distinct chemical abundances for the neutron-capture elements in M67-1315 and the lower metallicity of this star compared to M67-1194, indicate that the stars in M67 are likely not chemically homogeneous. This poses a challenge for the concept of chemical tagging since it is based on the assumption of stars forming in the same star-forming aggregate., Comment: 10 pages, 6 figures, accepted for publication in MNRAS
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- 2016
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24. The nucleosynthetic history of elements in the Galactic disk: [X/Fe] - age relations from high-precision spectroscopy
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Spina, L., Meléndez, J., Karakas, A. I., Ramírez, I., Monroe, T. R., Asplund, M., and Yong, D.
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Astrophysics - Solar and Stellar Astrophysics ,85A04 - Abstract
Context: The chemical composition of stars is intimately linked to the Galaxy formation and evolution. Aims: We aim to trace the chemical evolution of the Galactic disk through the inspection of the [X/Fe]-age relations of 24 species from C to Eu. Methods: Using high-resolution and high-signal-to-noise UVES spectra of nine solar twins, we obtained precise estimates of stellar ages and chemical abundances. These determinations have been integrated with additional accurate age and abundance determinations from recent spectroscopic studies of solar twins existing in the literature, comprising superb abundances with 0.01~dex precision. Based on this data set, we outlined the [X/Fe]-age relations over a time interval of 10~Gyr. Results: We present the [X/Fe] - age relations for 24 elements (C, O, Na, Mg, Al, Si, S, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Ba, La, Ce, Nd, and Eu). Each different class of elements showed distinct evolution with time that relies on the different characteristics, rates and timescales of the nucleosynthesis' sites from which they are produced. The $\alpha$-elements are characterised by a [X/Fe] decrement as time goes on. Strikingly, an opposite behaviour is observed for Ca. The iron-peak elements show an early [X/Fe] increase followed by a decrease towards the youngest stars. The [X/Fe] for the n-capture elements decrease with age. We also found that both [Mg/Y] and [Al/Y] are precise stellar clocks, with [Al/Y] showing the steepest dependence with age. Conslusions: Knowledge of the [X/Fe]-age relations is a gold mine from which we can achieve a great understanding about the processes that governed the formation and evolution of the Milky Way. Through the reverse engineering of these relations we will be able to put strong constraints on the nature of the stellar formation history, the SNe rates, the stellar yields, and the variety of the SNe progenitors., Comment: The paper has been accepted for publication by A&A
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- 2016
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25. The Solar Twin Planet Search III. The [Y/Mg] clock: estimating stellar ages of solar-type stars
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Maia, M. Tucci, Ramírez, I., Meléndez, J., Bedell, M., Bean, J. L., and Asplund, M.
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Astrophysics - Solar and Stellar Astrophysics - Abstract
Solar twins are stars with similar stellar (surface) parameters to the Sun that can have a wide range of ages. This provide an opportunity to analyze the variation of their chemical abundances with age. Nissen (2015) recently suggested that the abundances of the s-process element Y and the $\alpha$-element Mg could be used to estimate stellar ages. This paper aims to determine with high precision the Y, Mg, and Fe abundances for a sample of 88 solar twins that span a broad age range ($0.3-10.0$\,Gyr) and investigate their use for estimating ages. We obtained high-quality Magellan Inamori Kyocera Echelle (MIKE) spectra and determined Y and Mg abundances using equivalent widths and a line-by-line differential method within a 1D LTE framework. Stellar parameters and iron abundances were measured in Paper I of this series for all stars, but a few (three) required a small revision. The [Y/Mg] ratio shows a strong correlation with age. It has a slope of -0.041$\pm$0.001 dex/Gyr and a significance of 41 $\sigma$. This is in excellent agreement with the relation first proposed by Nissen (2015). We found some outliers that turned out to be binaries where mass transfer may have enhanced the yttrium abundance. Given a precise measurement of [Y/Mg] with typical error of 0.02 dex in solar twins, our formula can be used to determine a stellar age with $\sim$0.8 Gyr precision in the 0 to 10 Gyr range.
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- 2016
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26. The Hyades open cluster is chemically inhomogeneous
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Liu, F., Yong, D., Asplund, M., Ramirez, I., and Melendez, J.
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Astrophysics - Solar and Stellar Astrophysics - Abstract
We present a high-precision differential abundance analysis of 16 solar-type stars in the Hyades open cluster based on high resolution, high signal-to-noise ratio (S/N ~ 350 - 400) spectra obtained from the McDonald 2.7m telescope. We derived stellar parameters and differential chemical abundances for 19 elements (C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Ba) with uncertainties as low as ~ 0.01 - 0.02 dex. Our main results include: (1) there is no clear chemical signature of planet formation detected among the sample stars, i.e., no correlations in abundances versus condensation temperature; (2) the observed abundance dispersions are a factor of ~ 1.5 - 2 larger than the average measurement errors for most elements; (3) there are positive correlations, of high statistical significance, between the abundances of at least 90% of pairs of elements. We demonstrate that none of these findings can be explained by errors due to the stellar parameters. Our results reveal that the Hyades is chemically inhomogeneous at the 0.02 dex level. Possible explanations for the abundance variations include (1) inhomogeneous chemical evolution in the proto-cluster environment, (2) supernova ejection in the proto-cluster cloud, and (3) pollution of metal-poor gas before complete mixing of the proto-cluster cloud. Our results provide significant new constraints on the chemical composition of open clusters and a challenge to the current view of Galactic archeology., Comment: 17 pages, 17 figures, accepted for publication in MNRAS
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- 2016
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27. The detailed chemical composition of the terrestrial planet host Kepler-10
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Liu, F., Yong, D., Asplund, M., Ramirez, I., Melendez, J., Gustafsson, B., Howes, L. M., Roederer, I. U., Lambert, D. L., and Bensby, T.
- Subjects
Astrophysics - Solar and Stellar Astrophysics ,Astrophysics - Earth and Planetary Astrophysics - Abstract
Chemical abundance studies of the Sun and solar twins have demonstrated that the solar composition of refractory elements is depleted when compared to volatile elements, which could be due to the formation of terrestrial planets. In order to further examine this scenario, we conducted a line-by-line differential chemical abundance analysis of the terrestrial planet host Kepler-10 and fourteen of its stellar twins. Stellar parameters and elemental abundances of Kepler-10 and its stellar twins were obtained with very high precision using a strictly differential analysis of high quality CFHT, HET and Magellan spectra. When compared to the majority of thick disc twins, Kepler-10 shows a depletion in the refractory elements relative to the volatile elements, which could be due to the formation of terrestrial planets in the Kepler-10 system. The average abundance pattern corresponds to ~ 13 Earth masses, while the two known planets in Kepler-10 system have a combined ~ 20 Earth masses. For two of the eight thick disc twins, however, no depletion patterns are found. Although our results demonstrate that several factors (e.g., planet signature, stellar age, stellar birth location and Galactic chemical evolution) could lead to or affect abundance trends with condensation temperature, we find that the trends give further support for the planetary signature hypothesis., Comment: 12 pages, 11 figures, accepted for publication in MNRAS
- Published
- 2015
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28. The Solar Twin Planet Search II. A Jupiter twin around a solar twin
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Bedell, M., Melendez, J., Bean, J. L., Ramirez, I., Asplund, M., Alves-Brito, A., Casagrande, L., Dreizler, S., Monroe, T., Spina, L., and Maia, M. Tucci
- Subjects
Astrophysics - Earth and Planetary Astrophysics - Abstract
Through our HARPS radial velocity survey for planets around solar twin stars, we have identified a promising Jupiter twin candidate around the star HIP11915. We characterize this Keplerian signal and investigate its potential origins in stellar activity. Our analysis indicates that HIP11915 hosts a Jupiter-mass planet with a 3800-day orbital period and low eccentricity. Although we cannot definitively rule out an activity cycle interpretation, we find that a planet interpretation is more likely based on a joint analysis of RV and activity index data. The challenges of long-period radial velocity signals addressed in this paper are critical for the ongoing discovery of Jupiter-like exoplanets. If planetary in nature, the signal investigated here represents a very close analog to the solar system in terms of both Sun-like host star and Jupiter-like planet., Comment: 8 pages, 5 figures; A&A accepted; typos corrected in this version
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- 2015
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29. The dissimilar chemical composition of the planet-hosting stars of the XO-2 binary system
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Ramirez, I., Khanal, S., Aleo, P., Sobotka, A., Liu, F., Casagrande, L., Melendez, J., Yong, D., Lambert, D. L., and Asplund, M.
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Astrophysics - Solar and Stellar Astrophysics - Abstract
Using high-quality spectra of the twin stars in the XO-2 binary system, we have detected significant differences in the chemical composition of their photospheres. The differences correlate strongly with the elements' dust condensation temperature. In XO-2N, volatiles are enhanced by about 0.015 dex and refractories are overabundant by up to 0.090 dex. On average, our error bar in relative abundance is 0.012 dex. We present an early metal-depletion scenario in which the formation of the gas giant planets known to exist around these stars is responsible for a 0.015 dex offset in the abundances of all elements while 20 M_Earth of non-detected rocky objects that formed around XO-2S explain the additional refractory-element difference. An alternative explanation involves the late accretion of at least 20 M_Earth of planet-like material by XO-2N, allegedly as a result of the migration of the hot Jupiter detected around that star. Dust cleansing by a nearby hot star as well as age or Galactic birthplace effects can be ruled out as valid explanations for this phenomenon., Comment: ApJ, in press. Complete linelist (Table 3) available in the "Other formats -> Source" download
- Published
- 2015
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30. Shallow extra mixing in solar twins inferred from Be abundances
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Maia, M. Tucci, Meléndez, J., Castro, M., Asplund, M., Ramírez, I., Monroe, T. R., Nascimento Jr., J. D. do, and Yong, D.
- Subjects
Astrophysics - Solar and Stellar Astrophysics - Abstract
Lithium and beryllium are destroyed at different temperatures in stellar interiors. As such, their relative abundances offer excellent probes of the nature and extent of mixing processes within and below the convection zone. We determine Be abundances for a sample of eight solar twins for which Li abundances have previously been determined. The analyzed solar twins span a very wide range of age, 0.5-8.2 Gyr, which enables us to study secular evolution of Li and Be depletion. We gathered high-quality UVES/VLT spectra and obtained Be abundances by spectral synthesis of the Be II 313 nm doublet. The derived beryllium abundances exhibit no significant variation with age. The more fragile Li, however, exhibits a monotonically decreasing abundance with increasing age. Therefore, relatively shallow extra mixing below the convection zone is necessary to simultaneously account for the observed Li and Be behavior in the Sun and solar twins.
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- 2015
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31. Stellar Chemical Abundances: In Pursuit of the Highest Achievable Precision
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Bedell, M., Melendez, J., Bean, J., Ramirez, I., Leite, P., and Asplund, M.
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Astrophysics - Solar and Stellar Astrophysics ,Astrophysics - Earth and Planetary Astrophysics - Abstract
The achievable level of precision on photospheric abundances of stars is a major limiting factor on investigations of exoplanet host star characteristics, the chemical histories of star clusters, and the evolution of the Milky Way and other galaxies. While model-induced errors can be minimized through the differential analysis of spectrally similar stars, the maximum achievable precision of this technique has been debated. As a test, we derive differential abundances of 19 elements from high-quality asteroid-reflected solar spectra taken using a variety of instruments and conditions. We treat the solar spectra as being from unknown stars and use the resulting differential abundances, which are expected to be zero, as a diagnostic of the error in our measurements. Our results indicate that the relative resolution of the target and reference spectra is a major consideration, with use of different instruments to obtain the two spectra leading to errors up to 0.04 dex. Use of the same instrument at different epochs for the two spectra has a much smaller effect (~0.007 dex). The asteroid used to obtain the solar standard also has a negligible effect (~0.006 dex). Assuming that systematic errors from the stellar model atmospheres have been minimized, as in the case of solar twins, we confirm that differential chemical abundances can be obtained at sub-0.01 dex precision with due care in the observations, data reduction and abundance analysis., Comment: Accepted for publication in ApJ; 13 pages, 6 figures, 7 tables
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- 2014
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32. Influence of the power density and working pressure in the magnetron co-sputtering deposition of ZnO–SnO2 thin films and their effect in photocatalytic hydrogen production
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Saldaña-Ramírez, A., Cruz, M.R. Alfaro, Juárez-Ramírez, I., and Torres-Martínez, Leticia M.
- Published
- 2020
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33. The making of dendroclimatological knowledge : a symmetrical account of trust and scepticism in science
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Ramírez-i-Ollé, Meritxell, Sturdy, Steve, and Frow, Emma
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551.6 ,sociology of scientific knowledge ,dendroclimatology ,trust ,scepticism - Abstract
This thesis presents an empirical study of dendroclimatology, with the purpose of contributing to a wider understanding of the way scientists generate knowledge about climate change. Dendroclimatology is a science that produces knowledge about past climates from the analysis of tree growth. For two years, I have studied the work of a group of dendroclimatologists, joining them on fieldwork and sampling expeditions in the Scottish Highlands, observing how they generate data from tree samples to reconstruct past temperatures in Scotland and examining how they have mobilised a Scottish temperature reconstruction in a scientific debate over historical changes in climate. This thesis develops two parallel narratives about the practice of making dendroclimatological knowledge and the roles of trust and scepticism in this process. In describing how dendroclimatologists work to extract information about past climates from trees, I identify the importance of trust relationships and scepticism at each stage of their work. I conduct a symmetrical analysis of both trust and scepticism in science. In the past, scholars studying science have emphasised the critical role of either trust or scepticism in the construction of scientific knowledge, and have paid relatively little attention to examining the relationship between the two. In my study, I demonstrate that scepticism is part of the ordinary practice of dendroclimatology, and that scepticism in normal science (which I call “civil scepticism”) is fundamentally dependent (or “parasitic”) on existing trust relationships established through a variety of means. Dendroclimatologists engage in intimate interactions and mutual scrutiny of each other’s competence throughout the work they do in the field and in the laboratory, and they build upon and expand these trust relationships to create and defend climate reconstructions. I show that dendroclimatologists sustain trust relationships in part by demonstrating that they are competent sceptics (which I call “sceptical display”) and, in part by provisionally suspending their scepticism to permit agreement on what constitutes valid dendroclimatological knowledge. I also analyse how these internal practices of scepticism and agreement are influenced by sceptical challenges from actors external to the dendroclimatology community, including challenges grounded in similar trust relationships (a further instance of civil scepticism) and challenges that are not (which I call “uncivil scepticism”). I conclude that dendroclimatological knowledge is only possible as a result of contingent social negotiations over the distribution of trust and the boundaries of a trusting community.
- Published
- 2016
34. Non-convex non-local reactive flows for saliency detection and segmentation
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Galiano, G., Ramírez, I., and Schiavi, E.
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- 2020
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35. The Solar Twin Planet Search. I. Fundamental parameters of the stellar sample
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Ramirez, I., Melendez, J., Bean, J., Asplund, M., Bedell, M., Monroe, T., Casagrande, L., Schirbel, L., Dreizler, S., Teske, J., Maia, M. Tucci, Alves-Brito, A., and Baumann, P.
- Subjects
Astrophysics - Solar and Stellar Astrophysics - Abstract
We are carrying out a search for planets around a sample of solar twin stars using the HARPS spectrograph. The goal of this project is to exploit the advantage offered by solar twins to obtain chemical abundances of unmatched precision. This survey will enable new studies of the stellar composition -- planet connection. Here we used the MIKE spectrograph on the Magellan Clay Telescope to acquire high resolution, high signal-to-noise ratio spectra of our sample stars. We measured the equivalent widths of iron lines and used strict differential excitation/ionization balance analysis to determine atmospheric parameters of unprecedented internal precision (DTeff=7K, Dlogg=0.019, D[Fe/H]=0.006dex, Dvt=0.016km/s). Reliable relative ages and highly precise masses were then estimated using theoretical isochrones. The spectroscopic parameters we derived are in good agreement with those measured using other independent techniques. The root-mean-square scatter of the differences seen is fully compatible with the observational errors, demonstrating, as assumed thus far, that systematic uncertainties in the stellar parameters are negligible in the study of solar twins. We find a tight activity-age relation for our sample stars, which validates the internal precision of our dating method. Furthermore, we find that the solar cycle is perfectly consistent both with this trend and its star-to-star scatter. We present the largest sample of solar twins analyzed homogeneously using high quality spectra. The fundamental parameters derived from this work will be employed in subsequent work that aims to explore the connections between planet formation and stellar chemical composition., Comment: Astronomy and Astrophysics, in press
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- 2014
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36. VAMOS: a Pathfinder for the HAWC Gamma-Ray Observatory
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Abeysekara, A. U., Alfaro, R., Alvarez, C., Álvarez, J. D., Ángeles, F., Arceo, R., Arteaga-Velázquez, J. C., Avila-Aroche, A., Solares, H. A. Ayala, Badillo, C., Barber, A. S., Baughman, B. M., Bautista-Elivar, N., Gonzalez, J. Becerra, Belmont, E., Benítez, E., BenZvi, S. Y., Berley, D., Bernal, A., Rosales, M. Bonilla, Braun, J., Caballero-Lopez, R. A., Caballero-Mora, K. S., Cabrera, I., Carramiñana, A., Castañeda-Martínez, L., Castillo, M., Cotti, U., Cotzomi, J., de la Fuente, E., De León, C., DeYoung, T., Diaz-Azuara, A., Diaz-Cruz, L., Hernandez, R. Diaz, Díaz-Vélez, J. C., Dingus, B. L., Dultzin, D., DuVernois, M. A., Ellsworth, R. W., Fernandez, A., Fiorino, D. W., Fraija, N., Galindo, A., García-Torales, G., Garfias, F., González, A., González, L. X., González, M. M., Goodman, J. A., Grabski, V., Gussert, M., Guzmán-Cerón, C., Hampel-Arias, Z., Harding, J. P., Hernández-Cervantes, L., Hui, C. M., Hüntemeyer, P., Imran, A., Iriarte, A., Karn, P., Kieda, D., Kunde, G. J., Langarica, R., Lara, A., Lara, G., Lauer, R. J., Lee, W. H., Lennarz, D., Vargas, H. León, Linares, E. C., Linnemann, J. T., Longo, M., Luna-Garcia, R., Marinelli, A., Martínez, L. A., Martínez, H., Martínez, O., Martínez-Castro, J., Martos, M., Matthews, J. A. J., McEnery, J., Torres, E. Mendoza, Miranda-Romagnoli, P., Moreno, E., Mostafá, M., Nava, J., Nellen, L., Newbold, M., Noriega-Papaqui, R., Oceguera-Becerra, T., Page, D. P., Patricelli, B., Pelayo, R., Pérez-Pérez, E. G., Pretz, J., Ramírez, I., Renter, A., Rivière, C., Rosa-González, D., Ruiz-Sala, F., Ruiz-Velasco, E. L., Ryan, J., Sacahui, J. R., Salazar, H., Salesa, F., Sandoval, A., Santos, E., Schneider, M., Silich, S., Sinnis, G., Smith, A. J., Woodle, K. Sparks, Springer, R. W., Suarez, F., Taboada, I., Tepe, A., Toale, P. A., Tollefson, K., Torres, I., Tinoco, S., Ukwatta, T. N., Galicia, J. F. Valdés, Vanegas, P., Vázquez, A., Villaseñor, L., Wall, W., Weisgarber, T., Westerhoff, S., Wisher, I. G., Wood, J., Yodh, G. B., Younk, P. W., Zaborov, D., Zepeda, A., and Zhou, H.
- Subjects
Astrophysics - Instrumentation and Methods for Astrophysics - Abstract
VAMOS was a prototype detector built in 2011 at an altitude of 4100m a.s.l. in the state of Puebla, Mexico. The aim of VAMOS was to finalize the design, construction techniques and data acquisition system of the HAWC observatory. HAWC is an air-shower array currently under construction at the same site of VAMOS with the purpose to study the TeV sky. The VAMOS setup included six water Cherenkov detectors and two different data acquisition systems. It was in operation between October 2011 and May 2012 with an average live time of 30%. Besides the scientific verification purposes, the eight months of data were used to obtain the results presented in this paper: the detector response to the Forbush decrease of March 2012, and the analysis of possible emission, at energies above 30 GeV, for long gamma-ray bursts GRB111016B and GRB120328B., Comment: Accepted for pubblication in Astroparticle Physics Journal (20 pages, 10 figures). Corresponding authors: A.Marinelli and D.Zaborov
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- 2014
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37. 18 Sco: a solar twin rich in refractory and neutron-capture elements. Implications for chemical tagging
- Author
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Melendez, J., Ramirez, I., Karakas, A. I., Yong, D., Monroe, T. R., Bedell, M., Bergemann, M., Asplund, M., Maia, M. Tucci, Bean, J., Nascimento, J. -D. do, Bazot, M., Alves-Brito, A., Freitas, F. C., and Castro, M.
- Subjects
Astrophysics - Solar and Stellar Astrophysics ,Astrophysics - Earth and Planetary Astrophysics - Abstract
We study with unprecedented detail the chemical composition and stellar parameters of the solar twin 18 Sco in a strictly differential sense relative to the Sun. Our study is mainly based on high resolution (R ~ 110 000) high S/N (800-1000) VLT UVES spectra, which allow us to achieve a precision of about 0.005 dex in differential abundances. The effective temperature and surface gravity of 18 Sco are Teff = 5823+/-6 K and log g = 4.45+/-0.02 dex, i.e., 18 Sco is 46+/-6 K hotter than the Sun and log g is 0.01+/-0.02 dex higher. Its metallicity is [Fe/H] = 0.054+/-0.005 dex and its microturbulence velocity is +0.02+/-0.01 km/s higher than solar. Our precise stellar parameters and differential isochrone analysis show that 18 Sco has a mass of 1.04+/-0.02M_Sun and that it is ~1.6 Gyr younger than the Sun. We use precise HARPS radial velocities to search for planets, but none were detected. The chemical abundance pattern of 18 Sco displays a clear trend with condensation temperature, showing thus higher abundances of refractories in 18 Sco than in the Sun. Intriguingly, there are enhancements in the neutron-capture elements relative to the Sun. Despite the small element-to-element abundance differences among nearby n-capture elements (~0.02 dex), we successfully reproduce the r-process pattern in the solar system. This is independent evidence for the universality of the r-process. Our results have important implications for chemical tagging in our Galaxy and nucleosynthesis in general., Comment: ApJ, in press
- Published
- 2014
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38. Elemental Abundances of Solar Sibling Candidates
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Ramirez, I., Bajkova, A. T., Bobylev, V. V., Roederer, I. U., Lambert, D. L., Endl, M., Cochran, W. D., MacQueen, P. J., and Wittenmyer, R. A.
- Subjects
Astrophysics - Solar and Stellar Astrophysics - Abstract
Dynamical information along with survey data on metallicity and in some cases age have been used recently by some authors to search for candidates of stars that were born in the cluster where the Sun formed. We have acquired high resolution, high signal-to-noise ratio spectra for 30 of these objects to determine, using detailed elemental abundance analysis, if they could be true solar siblings. Only two of the candidates are found to have solar chemical composition. Updated modeling of the stars' past orbits in a realistic Galactic potential reveals that one of them, HD162826, satisfies both chemical and dynamical conditions for being a sibling of the Sun. Measurements of rare-element abundances for this star further confirm its solar composition, with the only possible exception of Sm. Analysis of long-term high-precision radial velocity data rules out the presence of hot Jupiters and confirms that this star is not in a binary system. We find that chemical tagging does not necessarily benefit from studying as many elements as possible, but instead from identifying and carefully measuring the abundances of those elements which show large star-to-star scatter at a given metallicity. Future searches employing data products from ongoing massive astrometric and spectroscopic surveys can be optimized by acknowledging this fact., Comment: ApJ, in press. Tables 2 and 4 are available in full in the "Other formats: source" download
- Published
- 2014
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39. A high precision chemical abundance analysis of the HAT-P-1 stellar binary: constraints on planet formation
- Author
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Liu, F., Asplund, M., Ramirez, I., Yong, D., and Melendez, J.
- Subjects
Astrophysics - Solar and Stellar Astrophysics ,Astrophysics - Earth and Planetary Astrophysics - Abstract
We present a high-precision, differential elemental abundance analysis of the HAT-P-1 stellar binary based on high-resolution, high signal-to-noise ratio Keck/HIRES spectra. The secondary star in this double system is known to host a transiting giant planet while no planets have yet been detected around the primary star. The derived metallicities ([Fe/H]) of the primary and secondary stars are identical within the errors: $0.146 \pm 0.014$ dex ($\sigma$ = 0.033 dex) and $0.155 \pm 0.007$ dex ($\sigma$ = 0.023 dex), respectively. Extremely precise differential abundance ratios of 23 elements have been measured (mean error of $\sigma$([X/Fe]) = 0.013 dex) and are found to be indistinguishable between the two stars: $\Delta$[X/Fe] (secondary - primary) = $+0.001 \pm 0.006$ dex ($\sigma$ = 0.008 dex). The striking similarity in the chemical composition of the two stellar components in HAT-P-1 is contrary to the possible 0.04 dex level difference seen in 16 Cyg A+B, which also hosts a giant planet, at least 3 times more massive than the one around HAT-P-1 secondary star. We conclude that the presence of giant planets does not necessarily imply differences in the chemical compositions of the host stars. The elemental abundances of each star in HAT-P-1 relative to the Sun show an identical, positive correlation with the condensation temperature of the elements; their abundance patterns are thus very similar to those observed in the majority of solar twins. In view of the Melendez et al. (2009)'s interpretation of the peculiar solar abundance pattern, we conclude that HAT-P-1 experienced less efficient formation of terrestrial planets than the Sun. This is in line with the expectation that the presence of close-in giant planets preventing the formation or survival of terrestrial planets., Comment: 5 pages, 2 figures, accepted for publication in MNRAS Letter
- Published
- 2014
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40. Chemical signatures of planets: beyond solar-twins
- Author
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Ramirez, I., Melendez, J., and Asplund, M.
- Subjects
Astrophysics - Solar and Stellar Astrophysics - Abstract
Elemental abundance studies of solar twin stars suggest that the solar chemical composition contains signatures of the formation of terrestrial planets in the solar system, namely small but significant depletions of the refractory elements. To test this hypothesis, we study stars which, compared to solar twins, have less massive convective envelopes (therefore increasing the amplitude of the predicted effect) or are, arguably, more likely to host planets (thus increasing the frequency of signature detections). We measure relative atmospheric parameters and elemental abundances of a late-F type dwarf sample (52 stars) and a sample of metal-rich solar analogs (59 stars). We detect refractory-element depletions with amplitudes up to about 0.15 dex. The distribution of depletion amplitudes for stars known to host gas giant planets is not different from that of the rest of stars. The maximum amplitude of depletion increases with effective temperature from 5650 K to 5950 K, while it appears to be constant for warmer stars (up to 6300 K). The depletions observed in solar twin stars have a maximum amplitude that is very similar to that seen here for both of our samples. Gas giant planet formation alone cannot explain the observed distributions of refractory-element depletions, leaving the formation of rocky material as a more likely explanation of our observations. More rocky material is necessary to explain the data of solar twins than metal-rich stars, and less for warm stars. However, the sizes of the stars' convective envelopes at the time of planet formation could be regulating these amplitudes. Our results could be explained if disk lifetimes were shorter in more massive stars, as independent observations indeed seem to suggest., Comment: Astronomy and Astrophysics, in press. Full tables available in the source download
- Published
- 2013
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41. Quantum Backflow States from Eigenstates of the Regularized Current Operator
- Author
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Halliwell, J. J., Gillman, E., Lennon, O., Patel, M., and Ramirez, I.
- Subjects
Quantum Physics - Abstract
We present an exhaustive class of states with quantum backflow -- the phenomenon in which a state consisting entirely of positive momenta may have negative current and the probability flows in the opposite direction to the momentum. They are characterized by a general function of momenta subject to very weak conditions. Such a family of states is of interest in the light of a recent experimental proposal to measure backflow. We find one particularly simple state which has surprisingly large backflow -- about 41 percent of the lower bound on flux derived by Bracken and Melloy. We study the eigenstates of a regularized current operator and we show how some of these states, in a certain limit, lead to our class of backflow states. This limit also clarifies the correspondence between the spectrum of the regularized current operator, which has just two non-zero eigenvalues in our chosen regularization, and the usual current operator., Comment: 16 pages, 2 figures
- Published
- 2013
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42. ‘Civil skepticism’ and the social construction of knowledge : A case in dendroclimatology
- Author
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Ramírez-i-Ollé, Meritxell
- Published
- 2018
43. Fatal Disseminated Infection by Trichosporon asahii Under Voriconazole Therapy in a Patient with Acute Myeloid Leukemia: A Review of Breakthrough Infections by Trichosporon spp.
- Author
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Ramírez, I. and Moncada, D.
- Published
- 2020
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44. VAMOS: A pathfinder for the HAWC gamma-ray observatory
- Author
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Abeysekara, AU, Alfaro, R, Alvarez, C, Álvarez, JD, Ángeles, F, Arceo, R, Arteaga-Velázquez, JC, Avila-Aroche, A, Solares, HA Ayala, Badillo, C, Barber, AS, Baughman, BM, Bautista-Elivar, N, Gonzalez, J Becerra, Belmont, E, Benítez, E, BenZvi, SY, Berley, D, Bernal, A, Rosales, M Bonilla, Braun, J, Caballero-Lopez, RA, Caballero-Mora, KS, Cabrera, I, Carramiñana, A, Castañeda-Martínez, L, Castillo, M, Cotti, U, Cotzomi, J, de la Fuente, E, De León, C, DeYoung, T, Diaz-Azuara, A, Diaz-Cruz, L, Hernandez, R Diaz, Díaz-Vélez, JC, Dingus, BL, Dultzin, D, DuVernois, MA, Ellsworth, RW, Fernandez, A, Fiorino, DW, Fraija, N, Galindo, A, García-Torales, G, Garfias, F, González, A, González, LX, González, MM, Goodman, JA, Grabski, V, Gussert, M, Guzmán-Cerón, C, Hampel-Arias, Z, Harding, JP, Hernández-Cervantes, L, Hui, CM, Hüntemeyer, P, Imran, A, Iriarte, A, Karn, P, Kieda, D, Kunde, GJ, Langarica, R, Lara, A, Lara, G, Lauer, RJ, Lee, WH, Lennarz, D, Vargas, H León, Linares, EC, Linnemann, JT, Longo, M, Luna-Garcia, R, Marinelli, A, Martínez, LA, Martínez, H, Martínez, O, Martínez-Castro, J, Martos, M, Matthews, JAJ, McEnery, J, Torres, E Mendoza, Miranda-Romagnoli, P, Moreno, E, Mostafá, M, Nava, J, Nellen, L, Newbold, M, Noriega-Papaqui, R, Oceguera-Becerra, T, Page, DP, Patricelli, B, Pelayo, R, Pérez-Pérez, EG, Pretz, J, Ramírez, I, Rentería, A, Rivière, C, and Rosa-González, D
- Subjects
Detector prototype ,Scientific verification ,TeV cosmic rays ,astro-ph.IM ,Astronomical and Space Sciences ,Atomic ,Molecular ,Nuclear ,Particle and Plasma Physics ,Nuclear & Particles Physics - Abstract
VAMOS1 was a prototype detector built in 2011 at an altitude of 4100 m a.s.l. in the state of Puebla, Mexico. The aim of VAMOS was to finalize the design, construction techniques and data acquisition system of the HAWC observatory. HAWC is an air-shower array currently under construction at the same site of VAMOS with the purpose to study the TeV sky. The VAMOS setup included six water Cherenkov detectors and two different data acquisition systems. It was in operation between October 2011 and May 2012 with an average live time of 30%. Besides the scientific verification purposes, the eight months of data were used to obtain the results presented in this paper: the detector response to the Forbush decrease of March 2012, and the analysis of possible emission, at energies above 30 GeV, for long gamma-ray bursts GRB111016B and GRB120328B.
- Published
- 2015
45. Oxygen Abundances in Nearby FGK Stars and the Galactic Chemical Evolution of the Local Disk and Halo
- Author
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Ramirez, I., Prieto, C. Allende, and Lambert, D. L.
- Subjects
Astrophysics - Solar and Stellar Astrophysics ,Astrophysics - Astrophysics of Galaxies - Abstract
Atmospheric parameters and oxygen abundances of 825 nearby FGK stars are derived using high-quality spectra and a non-LTE analysis of the 777 nm O I triplet lines. We assign a kinematic probability for the stars to be thin-disk (P1), thick-disk (P2), and halo (P3) members. We confirm previous findings of enhanced [O/Fe] in thick-disk (P2>0.5) relative to thin-disk (P1>0.5) stars with [Fe/H]<-0.2, as well as a "knee" that connects the mean [O/Fe]-[Fe/H] trend of thick-disk stars with that of thin-disk members at [Fe/H]>-0.2. Nevertheless, we find that the kinematic membership criterion fails at separating perfectly the stars in the [O/Fe]-[Fe/H] plane, even when a very restrictive kinematic separation is employed. Stars with "intermediate" kinematics (P1<0.7, P2<0.7) do not all populate the region of the [O/Fe]-[Fe/H] plane intermediate between the mean thin-disk and thick-disk trends, but their distribution is not necessarily bimodal. Halo stars (P3>0.5) show a large star-to-star scatter in [O/Fe]-[Fe/H], but most of it is due to stars with Galactocentric rotational velocity V<-200 km/s; halo stars with V>-200 km/s follow an [O/Fe]-[Fe/H] relation with almost no star-to-star scatter. Early mergers with satellite galaxies explain most of our observations, but the significant fraction of disk stars with "ambiguous" kinematics and abundances suggests that scattering by molecular clouds and radial migration have both played an important role in determining the kinematic and chemical properties of solar neighborhood stars., Comment: ApJ, in press. Complete tables 2-6 are available in the source (Download: Other formats -> Source)
- Published
- 2013
- Full Text
- View/download PDF
46. The infrared colors of the Sun
- Author
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Casagrande, L., Ramirez, I., Melendez, J., and Asplund, M.
- Subjects
Astrophysics - Solar and Stellar Astrophysics ,Astrophysics - Cosmology and Extragalactic Astrophysics ,Astrophysics - Earth and Planetary Astrophysics - Abstract
Solar infrared colors provide powerful constraints on the stellar effective temperature scale, but to this purpose they must be measured with both accuracy and precision. We achieve this requirement by using line-depth ratios to derive in a model independent way the infrared colors of the Sun, and use the latter to test the zero-point of the Casagrande et al. (2010) effective temperature scale, confirming its accuracy. Solar colors in the widely used 2MASS -J H K- and WISE -W1 W2 W3 W4- systems are provided. A cross check of the effective temperatures derived implementing 2MASS or WISE magnitudes in the infrared flux method confirms that the absolute calibration of the two systems agree within the errors, possibly suggesting a 1% offset between the two, thus validating extant near and mid infrared absolute calibrations. While 2MASS magnitudes are usually well suited to derive effective temperatures, we find that a number of bright, solar-like stars exhibit anomalous WISE colors. In most cases this effect is spurious and traceable to lower quality measurements, although for a couple of objects (3 +/- 2 % of the total sample) it might be real and hints towards the presence of warm/hot debris disks., Comment: ApJ, accepted. Minor changes to match published version
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- 2012
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47. Bio-crude oil production using catalytic hydrothermal liquefaction (HTL) from native microalgae harvested by ozone-flotation
- Author
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Nava Bravo, I., Velásquez-Orta, S.B., Cuevas-García, R., Monje-Ramírez, I., Harvey, A., and Orta Ledesma, M.T.
- Published
- 2019
- Full Text
- View/download PDF
48. Oxygen abundances in low- and high-alpha field halo stars and the discovery of two field stars born in globular clusters
- Author
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Ramirez, I., Melendez, J., and Chaname, J.
- Subjects
Astrophysics - Solar and Stellar Astrophysics ,Astrophysics - Astrophysics of Galaxies - Abstract
Oxygen abundances of 67 dwarf stars in the metallicity range -1.6<[Fe/H]<-0.4 are derived from a non-LTE analysis of the 777 nm O I triplet lines. These stars have precise atmospheric parameters measured by Nissen and Schuster, who find that they separate into three groups based on their kinematics and alpha-element (Mg, Si, Ca, Ti) abundances: thick-disk, high-alpha halo, and low-alpha halo. We find the oxygen abundance trends of thick-disk and high-alpha halo stars very similar. The low-alpha stars show a larger star-to-star scatter in [O/Fe] at a given [Fe/H] and have systematically lower oxygen abundances compared to the other two groups. Thus, we find the behavior of oxygen abundances in these groups of stars similar to that of the alpha elements. We use previously published oxygen abundance data of disk and very metal-poor halo stars to present an overall view (-2.3<[Fe/H]<+0.3) of oxygen abundance trends of stars in the solar neighborhood. Two field halo dwarf stars stand out in their O and Na abundances. Both G53-41 and G150-40 have very low oxygen and very high sodium abundances, which are key signatures of the abundance anomalies observed in globular cluster (GC) stars. Therefore, they are likely field halo stars born in GCs. If true, we estimate that at least 3+/-2% of the local field metal-poor star population was born in GCs., Comment: To appear in The Astrophysical Journal
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- 2012
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49. Lithium abundances in nearby FGK dwarf and subgiant stars: internal destruction, Galactic chemical evolution, and exoplanets
- Author
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Ramirez, I., Fish, J. R., Lambert, D. L., and Prieto, C. Allende
- Subjects
Astrophysics - Solar and Stellar Astrophysics - Abstract
We derive atmospheric parameters and lithium abundances for 671 stars and include our measurements in a literature compilation of 1381 dwarf and subgiant stars. First, a "lithium desert" in the effective temperature (Teff) versus lithium abundance (A_Li) plane is observed such that no stars with Teff~6075 K and A_Li~1.8 are found. We speculate that most of the stars on the low A_Li side of the desert have experienced a short-lived period of severe surface lithium destruction as main-sequence or subgiant stars. Next, we search for differences in the lithium content of thin-disk and thick-disk stars, but we find that internal processes have erased from the stellar photospheres their possibly different histories of lithium enrichment. Nevertheless, we note that the maximum lithium abundance of thick-disk stars is nearly constant from [Fe/H]=-1.0 to -0.1, at a value that is similar to that measured in very metal-poor halo stars (A_Li~2.2). Finally, differences in the lithium abundance distribution of known planet-host stars relative to otherwise ordinary stars appear when restricting the samples to narrow ranges of Teff or mass, but they are fully explained by age and metallicity biases. We confirm the lack of a connection between low lithium abundance and planets. However, we find that no low A_Li planet-hosts are found in the desert Teff window. Provided that subtle sample biases are not responsible for this observation, this suggests that the presence of gas giant planets inhibit the mechanism responsible for the lithium desert., Comment: ApJ, in press. Complete Tables 1 and 3 are available upon request
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- 2012
- Full Text
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50. Precise Effective Temperatures of Solar Analog Stars
- Author
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Cornejo, D., Ramirez, I., and Barklem, P. S.
- Subjects
Astrophysics - Solar and Stellar Astrophysics - Abstract
We perform a study of 62 solar analog stars to compute their effective temperatures (Teff) using the Balmer line wing fitting procedure and compare them with Teff values obtained using other commonly employed methods. We use observed H-alpha spectral lines and a fine grid of theoretical LTE model spectra calculated with the best available atomic data and most recent quantum theory. Our spectroscopic data are of very high quality and have been carefully normalized to recover the proper shape of the H-alpha line profile. We obtain Teff values with internal errors of about 25 K. Comparison of our results with those from other methods shows reasonably good agreement. Then, combining Teff values obtained from four independent techniques, we are able to determine final Teff values with errors of about 10 K., Comment: 4 pages, 4 figures, Comparative Magnetic Minima: Charactering proceedings of the IAU Symposium 286 on Comparative Magnetic Minima: Characterizing quiet times in the Sun and Stars, held in Mendoza, Argentina, October 3-7, 2011
- Published
- 2012
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