236 research outputs found
Multiple Acetylation of Pentaphenylferrocene â Synthesis and Asymmetric Reduction of 1âAcetylâ1â˛,2â˛,3â˛,4â˛,5â˛âpenta(paraâacetylphenyl)ferrocene
The FriedelâCrafts acetylation of pentaphenylferrocene has been revisited using 1.1 equivalents of AcCl/AlCl3 in CH2Cl2 at room temperature leading to the synthesis of 1âacetylâ1â˛,2â˛,3â˛,4â˛,5â˛âpentaphenylferrocene (78â% yield). Increased quantities of reagents and longer reaction times resulted in acetylation of the phenyl groups exclusively at the paraâposition, this methodology culminating in the synthesis of 1âacetylâ1â˛,2â˛,3â˛,4â˛,5â˛âpenta(paraâacetylphenyl)ferrocene (32â% for a two step process). Subsequent asymmetric reduction of all six ketone functionalities with BH3¡SMe2 catalysed by 60 molâ% (S)âCBS proceeded in 81â% yield to give (R,R,R,R,R,R)â1â(Îąâhydroxyethyl)â1â˛,2â˛,3â˛,4â˛,5â˛âpenta[paraâ(Îąâhydroxyethyl)phenyl]ferrocene, a highly functionalised enantiopure building block for the synthesis of ligands and materials
The Large Scale Distribution of Neutral Hydrogen in the Fornax Region
Using HIPASS data, we have searched for HI in a ~25x25 sq.deg. region centred
on the Fornax cluster. Within a velocity search range of 300 - 3700 km/s and a
lower flux limit of ~40 mJy, 110 galaxies with HI emission were detected, one
of which is previously uncatalogued. None of the detections has early-type
morphology. Previously unknown velocities for 14 galaxies have been determined,
with a further 4 velocity measurements being significantly dissimilar to
published values. Identification of an optical counterpart is relatively
unambiguous for more than ~90% of our HI galaxies. The galaxies appear to be
embedded in a sheet at the cluster velocity which extends for more than 30 deg
across the search area. At the nominal cluster distance of ~20 Mpc, this
corresponds to an elongated structure more than 10 Mpc in extent. A velocity
gradient across the structure is detected, with radial velocities increasing by
\~500 km/s from SE to NW. The clustering of galaxies evident in optical surveys
is only weakly suggested in the spatial distribution of our HI detections. Our
results suggest a considerable deficit of HI-rich galaxies in the centre of the
cluster. However, relative to the field, there is a 3(+/-1)-fold excess of
HI-rich galaxies in the outer parts of the cluster where galaxies may be
infalling towards the cluster for the first time.Comment: 16 pages, 14 figures, 110 HI spectra. To be published in MNRA
HIPASS Detection of an Intergalactic Gas Cloud in the NGC 2442 Group
We report the discovery, from the HI Parkes All-Sky Survey (HIPASS), of a gas
cloud associated with the asymmetric spiral galaxy NGC 2442. This object,
designated HIPASS J0731-69, contains ~10^9 M_sun of HI, or nearly one-third as
much atomic gas as NGC 2442 itself. No optical counterpart to any part of
HIPASS J0731-69 has yet been identified, consistent with the gas being diffuse,
and with its stream-like kinematics. If the gas in HIPASS J0731-69 was once
part of NGC 2442, then it was most likely a fairly recent tidal encounter with
a moderately massive companion which tore it loose, although the possibility of
ram-pressure stripping cannot be ruled out. This discovery highlights the
potential of the HIPASS data for yielding new clues to the nature of some of
the best-known galaxies in the local universe.Comment: 8 pages, 4 figures, uses "emulateapj5.sty". Accepted for publication
in ApJ, Vol. 555, 1 July 2001. Figs 1 and 2 included as JPE
The HIPASS Catalogue - II. Completeness, Reliability, and Parameter Accuracy
The HI Parkes All Sky Survey (HIPASS) is a blind extragalactic HI 21-cm
emission line survey covering the whole southern sky from declination -90 to
+25. The HIPASS catalogue (HICAT), containing 4315 HI-selected galaxies from
the region south of declination +2, is presented in Meyer et al. (2004a, Paper
I). This paper describes in detail the completeness and reliability of HICAT,
which are calculated from the recovery rate of synthetic sources and follow-up
observations, respectively. HICAT is found to be 99 per cent complete at a peak
flux of 84 mJy and an integrated flux of 9.4 Jy km/s. The overall reliability
is 95 per cent, but rises to 99 per cent for sources with peak fluxes >58 mJy
or integrated flux > 8.2 Jy km/s. Expressions are derived for the uncertainties
on the most important HICAT parameters: peak flux, integrated flux, velocity
width, and recessional velocity. The errors on HICAT parameters are dominated
by the noise in the HIPASS data, rather than by the parametrization procedure.Comment: Accepted for publication in MNRAS. 12 pages, 11 figures. Paper with
higher resolution figures can be downloaded from http://hipass.aus-vo.or
An Extragalactic HI Cloud with No Optical Counterpart?
We report the discovery, from the HI Parkes All-Sky Survey (HIPASS), of an
isolated cloud of neutral hydrogen which we believe to be extragalactic. The HI
mass of the cloud (HIPASS J1712-64) is very low, 1.7 x 10^7 Msun, using an
estimated distance of ~3.2 Mpc. Most significantly, we have found no optical
companion to this object to very faint limits (mu(B)~ 27 mag arcsec^-2). HIPASS
J1712-64 appears to be a binary system similar to, but much less massive than,
HI 1225+01 (the Virgo HI Cloud) and has a size of at least 15 kpc. The mean
velocity dispersion, measured with the Australia Telescope Compact Array
(ATCA), is only 4 km/s for the main component and because of the weak or
non-existent star-formation, possibly reflects the thermal linewidth (T<2000 K)
rather than bulk motion or turbulence. The peak column density for HIPASS
J1712-64, from the combined Parkes and ATCA data, is only 3.5 x 10^19 cm^-2,
which is estimated to be a factor of two below the critical threshold for star
formation. Apart from its significantly higher velocity, the properties of
HIPASS J1712-64 are similar to the recently recognised class of Compact High
Velocity Clouds. We therefore consider the evidence for a Local Group or
Galactic origin, although a more plausible alternative is that HIPASS J1712-64
was ejected from the interacting Magellanic Cloud/Galaxy system at
perigalacticon ~ 2 x 10^8 yr ago.Comment: 23 pages, 7 figures, AJ accepte
The 1000 Brightest HIPASS Galaxies: HI Mass Function and Omega_HI
We present a new accurate measurement of the HI mass function of galaxies
from the HIPASS Bright Galaxy Catalog, a sample of 1000 galaxies with the
highest HI peak flux densities in the southern hemisphere (Koribalski et al.
2003). This sample spans nearly four orders of magnitude in HI mass (from log
M_HI/M_sun=6.8 to 10.6, H0=75) and is the largest sample of HI selected
galaxies to date. We develop a bivariate maximum likelihood technique to
measure the space density of galaxies, and show that this is a robust method,
insensitive to the effects of large scale structure. The resulting HI mass
function can be fitted satisfactorily with a Schechter function with faint-end
slope alpha=-1.30. This slope is found to be dependent on morphological type,
with later type galaxies giving steeper slopes. We extensively test various
effects that potentially bias the determination of the HI mass function,
including peculiar motions of galaxies, large scale structure, selection bias,
and inclination effects, and quantify these biases. The large sample of
galaxies enables an accurate measurement of the cosmological mass density of
neutral gas: Omega_HI=(3.8 +/- 0.6) x 10^{-4}. Low surface brightness galaxies
contribute only 15% to this value, consistent with previous findings.Comment: accepted for publication in Astronomical Journal, 16 pages, including
17 figures. Corrected typos and reference
HIPASS High-Velocity Clouds: Properties of the Compact and Extended Populations
A catalog of Southern anomalous-velocity HI clouds at Decl. < +2 deg is
presented, based on data from the HI Parkes All-Sky Survey (HIPASS). The
improved sensitivity (5sigma: T_B = 0.04 K) and resolution (15.5') of the
HIPASS data results in a substantial increase in the number of individual
clouds (1956, as well as 41 galaxies) compared to previous surveys. Most
high-velocity emission features, HVCs, have a filamentary morphology and are
loosely organized into large complexes extending over tens of degrees. In
addition, 179 compact and isolated anomalous-velocity objects, CHVCs, are
identified based on their size and degree of isolation. 25% of the CHVCs
originally classified by Braun & Burton (1999) are reclassified. Both the
entire population of high-velocity emission features and the CHVCs alone have
typical HI masses of ~ 4.5 D(kpc)^2 solar masses and have similar slopes for
their column density and flux distributions. On the other hand, the CHVCs
appear to be clustered and the population can be broken up into three spatially
distinct groups, while the entire population of clouds is more uniformly
distributed with a significant percentage aligned with the Magellanic Stream.
The median velocities are V_GSR = -38 km/s for the CHVCs and -30 km/s for all
of the anomalous-velocity clouds. Based on the catalog sizes, high-velocity
features cover 19% of the southern sky and CHVCs cover 1%. (abridged)Comment: 32 pages, 26 figures in gif format, 2 ascii tables, to appear in the
Jan 2002 issue of The Astronomical Journal, high resolution version available
at http://origins.Colorado.EDU/~mputman/pubs.htm
SPLASH: The Southern Parkes Large-Area Survey in Hydroxyl -- Data Description & Release
We present the full data release for the Southern Parkes Large-Area Survey in
Hydroxyl (SPLASH), a sensitive, unbiased single-dish survey of the Southern
Galactic Plane in all four ground-state transitions of the OH radical at 1612,
1665, 1667 and 1720 MHz. The survey covers the inner Galactic Plane, Central
Molecular Zone and Galactic Centre over the range 2,
332 10, with a small extension between 2
6, 358 4. SPLASH is the most
sensitive large-scale survey of OH to-date, reaching a characteristic
root-mean-square sensitivity of mK for an effective velocity
resolution of km/s. The spectral line datacubes are optimised for the
analysis of extended, quasi-thermal OH, but also contain numerous maser
sources, which have been confirmed interferometrically and published elsewhere.
We also present radio continuum images at 1612, 1666 and 1720 MHz. Based on
initial comparisons with CO(J=1-0), we find that OH rarely extends
outside CO cloud boundaries in our data, but suggest that large variations in
CO-to-OH brightness temperature ratios may reflect differences in the total gas
column density traced by each. Column density estimation in the complex,
continuum-bright Inner Galaxy is a challenge, and we demonstrate how failure to
appropriately model sub-beam structure and the line-of-sight source
distribution can lead to order-of-magnitude errors. Anomalous excitation of the
1612 and 1720 MHz satellite lines is ubiquitous in the inner Galaxy, but is
disabled by line overlap in and around the Central Molecular Zone.Comment: Main paper: 22 pages, 15 figures. Online-only material (appended to
ArXiv PDF): 11 pages, 3 figure sets. Accepted to MNRAS. Survey data is
available from: https://docs.datacentral.org.au/splash
Stereoselective and Stereospecific Reactions of Cobalt Sandwich Complexes: Synthesis of a New Class of Single Enantiomer Bulky Planar Chiral PâN and PâP Ligands
Starting from (Ρ5-acetylcyclopentadienyl)(Ρ4-tetraphenylcyclobutadiene)cobalt(I), highly enantioselective (99â% ee) (S)-CBS catalysed ketone reduction followed by stereospecific alcohol-azide exchange, azide reduction and dimethyllation gave (R)-(Ρ5-Îą-N,N-dimethylaminoethylcyclopentadienyl)(Ρ4-tetraphenylcyclobutadiene) cobalt(I) (Arthursâ amine). This underwent highly diastereoselective cyclopalladation to give di-Îź-acetate-bis-(R)-[(Ρ5-(Sp)-2-(Îą-N,N-dimethylaminoethyl)cyclopentadienyl, 1-C, N)(Ρ4-tetraphenylcyclobutadiene)cobalt(I)]dipalladium, and highly diastereoselective lithiation to give (R)-(Ρ5-(Sp)-1-(Îą-N,N-dimethylaminoethyl)-2-(diphenylphosphino)cyclopentadienyl)(Ρ4-tetraphenylcyclobutadiene)cobalt(I) (PPCA) following the addition as electrophile of chlorodiphenylphosphine. This PN-ligand was converted into (R)-(Ρ5-(Sp)-1-(Îą-dicyclohexylphosphinoethyl)-2-(diphenylphosphino)cyclopentadienyl)(Ρ4-tetraphenylcyclobutadiene)cobalt(I), a PP-ligand (Rossiphos), by stereospecific amine-phosphine exchange using HPCy2. These air-stable PâN and PâP complexes are the first examples of a new class of bulky planar chiral ligands for application in asymmetric catalysis
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