799 research outputs found
Inhomogeneous states with checkerboard order in the t-J Model
We study inhomogeneous states in the t-J model using an unrestricted
Gutzwiller approximation. We find that checkerboard order, where
is a doping dependent number, emerges from Fermi surface instabilities of
both the staggered flux phase and the Fermi liquid state with realistic band
parameters. In both cases, the checkerboard order develops at wave vectors
, that are tied to the peaks of the
wave-vector dependent susceptibility, and is of the Lomer-Rice-Scott type. The
properties of such periodic, inhomogeneous states are discussed in connection
to the checkerboard patterns observed by STM in underdoped cuprates.Comment: Published Versio
Resolving the chemistry in the disk of TW Hydrae I. Deuterated species
We present Submillimeter Array (SMA) observations of several deuterated
species in the disk around the classical T Tauri star TW Hydrae at arcsecond
scales, including detections of the DCN J=3-2 and DCO+ J=3-2 lines, and upper
limits to the HDO 3(1,2)-2(2,1), ortho-H2D+ 1(1,0)-1(1,1) and para-D2H+
1(1,0)-1(0,1) transitions. We also present observations of the HCN J=3-2, HCO+
J=3-2 and H13CO+ J=4-3 lines for comparison with their deuterated
isotopologues. We constrain the radial and vertical distributions of various
species in the disk by fitting the data using a model where the molecular
emission from an irradiated accretion disk is sampled with a 2D Monte Carlo
radiative transfer code. We find that the distribution of DCO+ differs markedly
from that of HCO+. The D/H ratios inferred change by at least one order of
magnitude (0.01 to 0.1) for radii 70 AU and there is a rapid falloff
of the abundance of DCO+ at radii larger than 90 AU. Using a simple analytical
chemical model, we constrain the degree of ionization, x(e-)=n(e-)/n(H2), to be
~10^-7 in the disk layer(s) where these molecules are present. Provided the
distribution of DCN follows that of HCN, the ratio of DCN to HCN is determined
to be 1.7\pm0.5 \times 10^-2; however, this ratio is very sensitive to the
poorly constrained vertical distribution of HCN. The resolved radial
distribution of DCO+ indicates that {\it in situ} deuterium fractionation
remains active within the TW Hydrae disk and must be considered in the
molecular evolution of circumstellar accretion disks.Comment: 12 pages, 12 figures, accepted to Ap
An ALMA survey of DCN/HCN and DCO/HCO in protoplanetary disks
The deuterium enrichment of molecules is sensitive to their formation
environment. Constraining patterns of deuterium chemistry in protoplanetary
disks is therefore useful for probing how material is inherited or reprocessed
throughout the stages of star and planet formation. We present ALMA
observations at resolution of DCO, HCO, DCN, and
HCN in the full disks around T Tauri stars AS 209 and IM Lup, the
transition disks around T Tauri stars V4046 Sgr and LkCa 15, and the full disks
around Herbig Ae stars MWC 480 and HD 163296. We also present ALMA observations
of HCN in the IM Lup disk. DCN, DCO, and HCO are detected in all
disks, and HCN in all but the IM Lup disk. We find efficient deuterium
fractionation for the sample, with estimates of disk-averaged DCO/HCO
and DCN/HCN abundance ratios ranging from and ,
respectively, which is comparable to values reported for other ISM
environments. The relative distributions of DCN and DCO vary between disks,
suggesting that multiple formation pathways may be needed to explain the
diverse emission morphologies. In addition, gaps and rings observed in both
HCO and DCO emission provide new evidence that DCO bears a
complex relationship with the location of the midplane CO snowline.Comment: 36 pages, 14 figures, updated to match figure order of published
version in Ap
Influence of Aridity on Carbon Isotope Discrimination in Leaves of Stipa and Other C3 Species in Central Asian Grassland
Simultaneous Observations of Comet C/2002 T7 (LINEAR) with the Berkeley-Illinois-Maryland Association and Owens Valley Radio Observatory Interferometers: HCN and CH_3OH
We present observations of HCN J = 1-0 and CH_3OH J(K_a, K_c) = 3(1, 3)-4(0, 4) A+ emission from comet C/2002 T7 (LINEAR) obtained simultaneously with the Owens Valley Radio Observatory (OVRO) and Berkeley-Illinois-Maryland Association (BIMA) millimeter interferometers. We combined the data from both arrays to increase the (u, v) sampling and signal to noise of the detected line emission. We also report the detection of CH_3OH J(K_a, K_c) = 8(0, 8)-7(1, 7) A^+ with OVRO data alone. Using a molecular excitation code that includes the effects of collisions with water and electrons, as well as pumping by the Solar infrared photons (for HCN alone), we find a production rate of HCN of 2.9 × 10^(26) s^(–1) and for CH_3OH of 2.2 × 10^(27) s^(–1). Compared to the adopted water production rate of 3 × 10^(29) s^(–1), this corresponds to an HCN/H_2O ratio of 0.1% and a CH_3OH/H_2O ratio of 0.7%. We critically assess the uncertainty of these values due to the noise (~10%), the uncertainties in the adopted comet model (~50%), and the uncertainties in the adopted collisional excitation rates (up to a factor of 2). Pumping by Solar infrared photons is found to be a minor effect for HCN, because our 15" synthesized beam is dominated by the region in the coma where collisions dominate. Since the uncertainties in the derived production rates are at least as large as one-third of the differences found between comets, we conclude that reliable collision rates and an accurate comet model are essential. Because the collisionally dominated region critically depends on the water production rate, using the same approximate method for different comets may introduce biases in the derived production rates. Multiline observations that directly constrain the molecular excitation provide much more reliable production rates
- …