arXiv subjects

G. Gonzalez

Publications and source records attributed to G. Gonzalez.

28 records · Page 2Linked to original sources

arXiv2003

A Re-evaluation of the Super Li-rich Star in NGC 6633

We present a new abundance analysis of the super Li-rich star J37 and a comparison star in NGC 6633. We confirm the result of Deliyannis et al. that J37 has a Li abundance well above the meteoritic value, and we also confirm that Al, S, Si, Ca, Fe and Ni are super-solar, and C is sub-solar. We additionally find that Na, Sc, Ti are super-solar, while O is sub-solar. The abundance pattern of metals in J37 is generally consistent with the bulk composition of the Earth. We propose that accretion of circumstellar matter is the best explanation for these abundance anomalies, although we cannot rule out a secondary contribution from diffusion.

astro-ph↗

arXiv2003

Possible Post-AGB Stars

Radial velocities were measured for 5 potential post-AGB stars, two in the globular cluster NGC 1851 and three in the dSph galaxy Ursa Minor. All five potential PAGB stars were found to be radial velocity non-members.

astro-ph↗

arXiv2002

Optical and Infrared Photometry of the Unusual Type Ia Supernova 2000cx

We present optical and infrared photometry of the unusual Type Ia supernova 2000cx. With the data of Li et al. (2001) and Jha (2002), this comprises the largest dataset ever assembled for a Type Ia SN, more than 600 points in UBVRIJHK. We confirm the finding of Li et al. regarding the unusually blue B-V colors as SN 2000cx entered the nebular phase. Its I-band secondary hump was extremely weak given its B-band decline rate. The V minus near infrared colors likewise do not match loci based on other slowly declining Type Ia SNe, though V-K is the least ``abnormal''. In several ways SN 2000cx resembles other slow decliners, given its B-band decline rate (Delta m_15(B) = 0.93), the appearance of Fe III lines and weakness of Si II in its pre-maximum spectrum, the V-K colors and post-maximum V-H colors. If the distance modulus derived from Surface Brightness Fluctuations of the host galaxy is correct, we find that the rate of light increase prior to maximum, the characteristics of the bolometric light curve, and the implied absolute magnitude at maximum are all consistent with a sub-luminous object with Delta m_15(B) ~ 1.6-1.7 having a higher than normal kinetic energy.

astro-ph↗

arXiv2002

Stellar Atmospheres of Nearby Young Solar Analogs

High-resolution (R ~ 90,000) spectra of 34 nearby, young Sun-like stars were analyzed using stellar atmosphere models to estimate effective photosphere temperatures, surface gravities, and the abundance of certain heavy elements (C, Na, Mg, Si, S, Ca, Ti, Fe, and Ni). The effective temperatures derived from spectroscopy were compared with temperatures estimated using optical and near-infrared photometry. In many cases the spectroscopic temperatures are significantly higher than the photometric estimates, possibly as a result of spottedness or chromospheric activity on these active stars. Values of effective temperature, surface gravity, and luminosity were compared to theoretical stellar evolution tracks and the evolutionary status of these objects was evaluated. The correlation between heavy element abundance patterns and kinematics (space motion) was also examined. Two nearby stars that were tentatively assigned to the Hyades cluster based on kinematics have Fe abundances that are also consistent with membership in that cluster. Members of the Ursa Major kinematic group exhibit a range of [Fe/H] values but have monotonic [Si/Fe]. These two observations suggest that heterogeneous incorporation of the heavy elements into protostars is creating the variation in metallicity. Local Association members have a distinctly different Si/Fe that probably reflects their distinct origin and chemical inheritance.

astro-ph↗

arXiv2001

Readout and Control of a Power-recycled Interferometric Gravitational-wave Antenna

Interferometric gravitational wave antennas are based on Michelson interferometers whose sensitivity to small differential length changes has been enhanced by adding multiple coupled optical resonators. The use of optical cavities is essential for reaching the required sensitivity, but sets challenges for the control system which must maintain the cavities near resonance. The goal for the strain sensitivity of the Laser Interferometer Gravitational-wave Observatory (LIGO) is 10^-21 rms, integrated over a 100 Hz bandwidth centered at 150 Hz. We present the major design features of the LIGO length and frequency sensing and control system which will hold the differential length to within 5 10^-14 m of the operating point. We also highlight the restrictions imposed by couplings of noise into the gravitational wave readout signal and the required immunity against them.

physics.ins-det↗

arXiv2001

Spectroscopic Analysis of Two Carbon Rich Post-AGB Stars

The chemical compositions of the C-rich pAGB stars IRAS 05113+1347 and IRAS 22272+5424 are determined from high-resolution optical spectra using standard LTE model atmosphere-based techniques. The stars are C, N, and $s$-process enriched suggesting efficient operation of the third-dredge up in the AGB star following a first dredge-up that increased the N abundance. Lithium is present with an abundance requiring Li manufacture. With this pair, abundance analyses are now available for 11 C-rich pAGBs. A common history is indicated and, in particular, the $s$-abundances, especially the relative abundances of light to heavy $s$-process elements, follow recent predictions for the third dredge-up in AGB stars.

astro-ph↗

arXiv2000

Parent Stars of Extrasolar Planets VI: Abundance Analyses of 20 New Systems

The results of new spectroscopic analyses of 20 recently reported extrasolar planet parent stars are presented. The companion of one of these stars, HD 10697, has recently been shown to have a mass in the brown dwarf regime; we find [Fe/H] $= +0.16$ for it. For the remaining sample, we derive [Fe/H] estimates ranging from -0.41 to $+0.37$, with an average value of $+0.18 \pm 0.19$. If we add the 13 stars included in the previous papers of this series and 6 other stars with companions below the 11 M$_{\rm Jup}$ limit from the recent studies of Santos et al., we derive $<$[Fe/H]$> = +0.17 \pm 0.20$. Among the youngest stars with planets with F or G0 spectral types, [Fe/H] is systematically larger than young field stars of the same Galactocentric distance by 0.15 to 0.20 dex. This confirms the recent finding of Laughlin that the most massive stars with planets are systematically more metal rich than field stars of the same mass. We interpret these trends as supporting a scenario in which these stars accreted high-Z material after their convective envelopes shrunk to near their present masses. Correcting these young star metallicities by 0.15 dex still does not fully account for the difference in mean metallicity between the field stars and the full parent stars sample. The stars with planets appear to have smaller [Na/Fe], [Mg/Fe], and [Al/Fe] values than field dwarfs of the same [Fe/H]. They do not appear to have significantly different values of [O/Fe], [Si/Fe], [Ca/Fe], or [Ti/Fe], though.

astro-ph↗

arXiv2000

The Chemical Compositions of the SRd Variable Stars. III. KK Aquilae, AG Aurigae, Z Aurigae, W Leo Minoris, and WW Tauri

Chemical compositions are derived from high-resolution spectra for five field SRd variables. These supergiants not previously analysed are shown to be metal-poor: KK Aql with [Fe/H] = -1.2, AG Aur with [Fe/H] = -1.8, Z Aur with [Fe/H] = -1.4, W LMi with [Fe/H] = -1.1, and WW Tau with [Fe/H] = -1.1. Their compositions are, except for two anomalies, identical to within the measurement errors with the compositions of subdwarfs, subgiants, and less evolved giants of the same [Fe/H]. One anomaly is an s-process enrichment for KK Aql, the first such enrichment reported for a SRd variable. The second and more remarkable anomaly is a strong lithium enrichment for W LMi, also a first for field SRds. The Li I 6707 A profile is not simply that of a photospheric line but includes strong absorption from red-shifted gas, suggesting, perhaps, that lithium enrichment results from accretion of Li-rich gas. This potential clue to lithium enrichment is discussed in light of various proposals for lithium synthesis in evolved stars.

astro-ph↗

arXiv1999

Toward gravitational wave detection

An overview of some tools and techniques being developed for data conditioning (regression of instrumental and environmental artifacts from the data channel), detector design evaluation (modeling the science ``reach'' of alternative detector designs and configurations), noise simulations for mock data challenges and analysis system validation, and analyses for the detection of gravitational radiation from gamma-ray burst sources.

gr-qc↗

arXiv1999

Parent Stars of Extrasolar Planets V: HD75289

The results of a new spectroscopic analysis of HD75289, recently reported to harbor a Jovian-mass planet, are presented. From high-resolution, high-S/N ratio spectra, we derive [Fe/H] = +0.28 +/- 0.05 for this star, in agreement with the spectroscopic study of Gratton et al., published 10 years ago. In addition, we present a re-analysis of the spectra of Upsilon And and Tau Boo; our new parameters for these two stars are now in better agreement with photometrically-derived values and with the recent spectroscopic analyses of Fuhrmann, et al. We also report on extended abundance analyses of 14 Her, HD187123, HD210277, and Rho Cnc. If we include the recent spectroscopic analyses of HD217107 by Randich et al. and Sadakane et al., who both reported [Fe/H] ~ +0.30 for this star, we can state that all the "hot-Jupiter" systems studied to date have metal-rich parent stars. We find that the mean [C/Fe] and [Na/Fe] values among the stars-with-planets sample are smaller than the corresponding quantities among field stars of the same [Fe/H].

astro-ph↗