Publications (45)
uvby- photometry of solar twins: the solar colors, model atmospheres, and the Teff and metallicity scales
J. Melendez, W. J. Schuster, J. S. Silva +3
Solar colors have been determined on the uvby- photometric system to test absolute solar fluxes, to examine colors predicted by model atmospheres as a function of stellar param…
The dissimilar chemical composition of the planet-hosting stars of the XO-2 binary system
I. Ramirez, S. Khanal, P. Aleo +7
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…
The Li-age correlation: the Sun is unusually Li deficient for its age
M. Carlos, J. Melendez, L. Spina +8
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 exoplan…
Granulation in K-type Dwarf Stars. I. Spectroscopic observations
I. Ramirez, C. Allende Prieto, D. L. Lambert
Very high resolution (R~160,000-210,000), high signal-to-noise ratio (S/N>300) spectra of nine bright K-dwarfs were obtained with the 2dcoude spectrograph on the 2.7m Telescope at…
The infrared colors of the Sun
L. Casagrande, I. Ramirez, J. Melendez +1
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 achiev…
Permitted Oxygen Abundances and the Temperature Scale of Metal-Poor Turn-Off Stars
J. Melendez, N. G. Shchukina, I. E. Vasiljeva +1
We use high quality VLT/UVES published data of the permitted OI triplet and FeII lines to determine oxygen and iron abundances in unevolved (dwarfs, turn-off, subgiants) metal-poor…
Chemical signatures of planets: beyond solar-twins
I. Ramirez, J. Melendez, M. Asplund
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…
Detailed chemical compositions of planet hosting stars: I. Exploration of possible planet signatures
F. Liu, D. Yong, M. Asplund +5
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 us…
A possible signature of terrestrial planet formation in the chemical composition of solar analogs
I. Ramirez, M. Asplund, P. Baumann +2
Recent studies have shown that the elemental abundances in the Sun are anomalous when compared to most (about 85%) nearby solar twin stars. Compared to its twins, the Sun exhibits…
The Hyades open cluster is chemically inhomogeneous
F. Liu, D. Yong, M. Asplund +2
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)…
Granulation signatures in the spectrum of the very metal-poor red giant HD122563
I. Ramirez, R. Collet, D. L. Lambert +2
A very high resolution (R=200,000), high signal-to-noise ratio (S/N=340) blue-green spectrum of the very metal-poor ([Fe/H]=-2.6) red giant star HD122563 has been obtained by us at…
iota Horologii is unlikely to be an evaporated Hyades star
I. Ramirez, D. Yong, E. Gutierrez +3
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…
The solar, exoplanet and cosmological lithium problems
J. Melendez, I. Ramirez, L. Casagrande +6
We review three Li problems. First, the Li problem in the Sun, for which some previous studies have argued that it may be Li-poor compared to other Suns. Second, we discuss the Li…
The chemical composition of HIP34407/HIP34426 and other twin-star comoving pairs
I. Ramirez, S. Khanal, S. J. Lichon +4
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…
The Solar Twin Planet Search II. A Jupiter twin around a solar twin
M. Bedell, J. Melendez, J. L. Bean +8
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 K…
Fundamental Parameters and Abundances of Metal-Poor Stars: The SDSS Standard BD +17 4708
I. Ramirez, C. Allende Prieto, S. Redfield +1
The atmospheric parameters and iron abundance of the Sloan Digital Sky Survey (SDSS) spectrophotometric standard star BD +17 4708 are critically examined using up-to-date Kurucz mo…
Oxygen in Galactic Disk Stars: non-LTE abundances from the 777 nm O I triplet
I. Ramirez, C. Allende Prieto, D. L. Lambert
Oxygen abundances for a large sample of dwarf and giant stars kinematically selected to be part of the Galactic thin and thick disks have been determined from a non-LTE analysis of…
Fundamental Parameters and Chemical Composition of Arcturus
I. Ramirez, C. Allende Prieto
We derive a self-consistent set of atmospheric parameters and abundances of 17 elements for the red giant star Arcturus: Teff = 4286+/-30 K, logg = 1.66+/-0.05, and [Fe/H] = -0.52+…
Large excess of heavy nitrogen in both hydrogen cyanide and cyanogen from comet 17P/Holmes
D. Bockelée-Morvan, N. Biver, E. Jehin +15
From millimeter and optical observations of the Jupiter-family comet 17P/Holmes performed soon after its huge outburst of October 24, 2007, we derive 14 N/15N = 139 +/- 26 in HCN,…
18 Sco: a solar twin rich in refractory and neutron-capture elements. Implications for chemical tagging
J. Melendez, I. Ramirez, A. I. Karakas +12
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 mainl…
Observational signatures for depletion in the Spite plateau: solving the cosmological Li discrepancy?
J. Melendez, L. Casagrande, I. Ramirez +2
We present Li abundances for 73 stars in the metallicity range -3.5 < [Fe/H] < -1.0 using improved IRFM temperatures (Casagrande et al. 2010) with precise E(B-V) values obtained mo…
Granulation across the HR diagram
I. Ramirez, C. Allende Prieto, D. L. Lambert +2
We have obtained ultra-high quality spectra (R=180,000; S/N>300) with unprecedented wavelength coverage (4400 to 7400 A) for a number of stars covering most of the HR diagram in or…
Precise Effective Temperatures of Solar Analog Stars
D. Cornejo, I. Ramirez, P. S. Barklem
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 u…
The chemical compositions of solar twins in the open cluster M67
F. Liu, M. Asplund, D. Yong +5
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…
A high precision chemical abundance analysis of the HAT-P-1 stellar binary: constraints on planet formation
F. Liu, M. Asplund, I. Ramirez +2
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 se…
Quantum Backflow States from Eigenstates of the Regularized Current Operator
J. J. Halliwell, E. Gillman, O. Lennon +2
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 probabil…
Chemical similarities between Galactic bulge and local thick disk red giants: O, Na, Mg, Al, Si, Ca and Ti
A. Alves-Brito, J. Melendez, M. Asplund +2
... We confirm the well-established differences for [/Fe] at a given metallicity between the local thin and thick disks. For all the elements investigated, we find no chemical…
Unprecedented accurate abundances: signatures of other Earths?
J. Melendez, M. Asplund, B. Gustafsson +2
For more than 140 years the chemical composition of our Sun has been considered typical of solar-type stars. Our highly differential elemental abundance analysis of unprecedented a…
IRFM T_eff calibrations for cluster and field giants in the Vilnius, Geneva, RI(C) and DDO photometric systems
I. Ramirez, J. Melendez
Based on a large sample of disk and halo giant stars, for which accurate effective temperatures derived through the InfraRed Flux Method (IRFM) exist, a calibration of the temperat…
Stellar Chemical Abundances: In Pursuit of the Highest Achievable Precision
M. Bedell, J. Melendez, J. Bean +3
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…
The UBV(RI)c colors of the Sun
I. Ramirez, R. Michel, R. Sefako +6
Photometric data in the UBV(RI)c system have been acquired for 80 solar analog stars for which we have previously derived highly precise atmospheric parameters Teff, log g, and [Fe…
Does the anomalous solar chemical composition come from planet formation?
I. Ramirez, J. Melendez, M. Asplund
We derive the abundance of 19 elements in a sample of 64 stars with fundamental parameters very similar to solar, which minimizes the impact of systematic errors in our spectroscop…
Chemical similarities between Galactic bulge and local thick disk red giant stars
J. Melendez, M. Asplund, A. Alves-Brito +8
The evolution of the Milky Way bulge and its relationship with the other Galactic populations is still poorly understood. The bulge has been suggested to be either a merger-driven…
The detailed chemical composition of the terrestrial planet host Kepler-10
F. Liu, D. Yong, M. Asplund +7
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 coul…
Lithium abundances in nearby FGK dwarf and subgiant stars: internal destruction, Galactic chemical evolution, and exoplanets
I. Ramirez, J. R. Fish, D. L. Lambert +1
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 d…
Granulation in K-type Dwarf Stars. II. Hydrodynamic simulations and 3D spectrum synthesis
I. Ramirez, C. Allende Prieto, L. Koesterke +2
We construct a 3D radiative-hydrodynamic model atmosphere of parameters Teff = 4820 K, log g = 4.5, and solar chemical composition. The theoretical line profiles computed with this…
Oxygen Abundances in Nearby Stars. Clues to the formation and evolution of the Galactic disk
I. Ramirez, C. Allende Prieto, D. L. Lambert
The abundances of iron and oxygen are homogeneously determined in a sample of 523 nearby (d<150 pc) FGK disk and halo stars with metallicities in the range -1.5<[Fe/H]<0.5. The oxy…
Elemental abundance differences in the 16 Cygni binary system: a signature of gas giant planet formation?
I. Ramirez, J. Melendez, D. Cornejo +2
The atmospheric parameters of the components of the 16Cygni binary system, in which the secondary has a gas giant planet detected, are measured accurately using high quality observ…
Signatures of Granulation in the Spectra of K-Dwarfs
I. Ramirez, C. Allende Prieto, D. L. Lambert +1
Very high resolution (R>150,000) spectra of a small sample of nearby K-dwarfs have been acquired to measure the line asymmetries and central wavelength shifts caused by convective…
An absolutely calibrated effective temperature scale from the InfraRed Flux Method
L. Casagrande, I. Ramirez, J. Melendez +2
Various effective temperature scales have been proposed over the years. Despite much work and the high internal precision usually achieved, systematic differences of order 100 K (o…
The Solar Twin Planet Search. I. Fundamental parameters of the stellar sample
I. Ramirez, J. Melendez, J. Bean +10
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 twi…
Accounting for Convective Blue-Shifts in the Determination of Absolute Stellar Radial Velocities
C. Allende Prieto, L. Koesterke, I. Ramirez +2
For late-type non-active stars, gravitational redshifts and convective blueshifts are the main source of biases in the determination of radial velocities. If ignored, these effects…
Elemental Abundances of Solar Sibling Candidates
I. Ramirez, A. T. Bajkova, V. V. Bobylev +6
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 cl…
Oxygen Abundances in Nearby FGK Stars and the Galactic Chemical Evolution of the Local Disk and Halo
I. Ramirez, C. Allende Prieto, D. L. Lambert
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 kine…
Oxygen abundances in low- and high-alpha field halo stars and the discovery of two field stars born in globular clusters
I. Ramirez, J. Melendez, J. Chaname
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 atmosphe…