Transcript ALMA How does it work and how to use it

ALMA
How does it work and how to use it?
Dr. Lizette Guzman-Ramirez
ESO Fellow for ALMA
What is ALMA?
• Atacama Large Millimeter and sub-millimeter Array.
ALMA as an Interferometer
• 66 antennas working as one radiotelescope.
• Is as if we had a 15km radiotelescope.
ALMA as an Interferometer
• ALMA is 10-100 times more sensitive and have 10-100
times better angular resolution than existing instruments.
• Total cost US$ 1.3 billions
How interferometry works
D
B
• One antenna the
resolution goes λ/D,
where D is the diameter
of the antenna.
• Two antennas the resolution
goes λ/B, where B is the
baseline between the two
antennas.
How interferometry works
Interferometry
How interferometry works
• The 66 antennas and electronics working with a
precision of one picosecond (10-12s).
• The signals from the different antennas must be
combined in a way that the path followed from each
antenna until it is combined at the central computer
(the correlator) must be known with an accuracy equal
to the diameter of a human hair (10-9m).
• Seven weather stations, and specially-built Water
Vapor Radiometers (WVR) to measure the amount of
line-of-sight water vapor present in the atmosphere,
will be used to correct for the atmospheric effects.
The antennas are moved using a
transporter
Main parts of an ALMA antenna
• Antenna
– It captures and concentrates
the radio waves coming from
the astronomical source at the
point known as the focus. The
light is reflected by a second
reflecting surface –called a
subreflector- to a point behind
the parabolic surface, where
there is a receiver geared to
capture the signal concentrated
by the antenna.
54 (12m) and 12 (7m) antennas
12m Array
Baseline (BL)
7m Array
Atacama Compact Array (ACA)
The Front End is where the signal gets
amplified, it has to be cooled to 4K
The Back End to the central computer (correlator), and subsequently transmits it to the
central building.
The correlator is the fastest
supercomputer that take the signals from
the antennas and combine them
ALMA bands
ALMA bands
ALMA Band
Frequency (GHz)
1
31 - 45
2
67 - 90
3
84 - 116
4
125 - 163
5
163 - 211
6
211 - 275
7
275 - 373
8
385 - 500
9
602 - 720
10
787 - 950
ALMA bands
Main molecules per band
ALMA Band
Frequency (GHz)
Main Lines
1
31 - 45
2
67 - 90
3
84 - 116
CO(1-0)
4
125 - 163
H2O
5
163 - 211
6
211 - 275
CO (2-1)
7
275 - 373
CO (3-2), [CII] z=5
8
385 - 500
CO (4-3), [CII] z=3
9
602 - 720
CO (6-5), [CII] z=2
10
787 - 950
CO (7-6), CO (8-7)
Splatalogue
• The splatalogue catalog is maintained by
NRAO and is a compilation from several
databases for molecular and atomic lines.
Many spectral lines are listed in it, so it is a
very useful tool in planning observations for
ALMA.
• http://www.splatalogue.net
Splatalogue
Observing modes
• The telescope can be set in “frequency division
mode” (FDM), which means that high spectral
resolution can be reached but with bandwidth,
quantization, and Nyquist sampling restrictions.
• In the “time division mode” (TDM), the entire 2
GHz bandwidth is used at 3 bit level quantization.
This mode is used to observe continuum
Velocity resolution per band
per observing mode
Spatial resolution per frequency
This depends on the baseline, for this case 1km baseline
was used for bands 3-7 and 1.5km for 8 & 9. For Cycle 3
longer baselines will be offered, up to 15km
(resolution is roughly an order of magnitude better)
For a baseline of 16km at 650GHz the
resolution is 0.005” (5marcsec)
Science goals
•
•
•
•
ALMA Deep Field – High-z galaxies
Star and Planet formation
Chemistry in molecular clouds
Map gas and dust in the Milky Way and other
galaxies
• Evolved starts – dust formation
• The Sun – origin of solar wind
ALMA discoveries
• Multiwavelength
composite of the
Antennae, showing their
namesake tidal tails in
radio (blues), past and
recent starbirths in optical
(whites and pinks) ALMA’s
first mm/submm test
views, in Bands 3 (orange),
6 (amber), & 7 (yellow),
showing detail surpassing
all other views in these
wavelengths.
ALMA discoveries
• The dust ring around the
bright star Fomalhaut.
The underlying blue
picture shows an earlier
picture obtained the
HST. The new ALMA
image has given
astronomers a major
breakthrough in
understanding a nearby
planetary system and
provided valuable clues
about how such systems
form and evolve.
ALMA discoveries
• A spiral structure around
the old star R Sculptoris.
This feature has never
been seen before and is
probably caused by a
hidden companion star
orbiting the star. This slice
through the new ALMA
data reveals the shell
around the star, which
shows up as the outer
circular ring, as well as a
very clear spiral structure
in the inner material.
ALMA discoveries
• This composite shows the region around the massive star-forming
region SDC 335.579-0.292. The Spitzer view is at infrared wavelengths
(3.6, 4.5 and 8.0 microns) and the ALMA view is at wavelengths around
three millimeters. The yellow blob at the center of the ALMA images is
a stellar womb with over 500 times the mass than the Sun. The
embryonic star is feeding on the material that is racing inwards. It is
expected to give birth to a 100Mo star.
ALMA discoveries
• Observations of CO fog
by hunting for a
different molecule
known as diazenylium
(N2H+). This fragile
molecule is easily
destroyed in the
presence of CO gas, so
would only appear in
detectable amounts in
regions where CO had
frozen out, and is
hence a proxy for CO
ice.
ALMA discoveries
• This image from ALMA
shows the distribution of
molecular gas close to the
supermassive black hole
at the centre of the
galaxy NGC 1433. As well
as discovering the spiral
structure ALMA
observations have also
revealed an unexpected
small outflow of material
from the central black
hole.
ALMA discoveries
• ALMA data (in
red) shows newly
formed dust in the
center of the
remnant. HST (in
green) and
Chandra (in blue)
show the
expanding
shockwave.
ALMA discoveries
• Dust and gas disk around
HD142527. The dust and
gas distributions observed
by ALMA are shown in red
and green, respectively.
Near-infrared image taken
by the NAOJ Subaru
Telescope is shown in blue.
The image clearly shows
that the dust is
concentrated in the
northern (upper) part of
the disk.
ALMA discoveries
• Detection of radio emission from GRB host galaxies, which had
been a long-sought goal for astronomers, was finally made
possible by ALMA with its unprecedentedly high sensitivity.
ALMA discoveries
• ALMA Pinpoints
Pluto to Help
Guide NASA’s New
Horizons
Spacecraft. The
cold surface of
Pluto and its
largest moon
Charon as seen
with ALMA on July
15, 2014.
ALMA discoveries
• The sharpest image ever
taken by ALMA. It shows
the protoplanetary disc
surrounding the young star
HL Tauri. These new ALMA
observations reveal
substructures within the
disc that have never been
seen before and even
show the possible
positions of planets
forming in the dark
patches within the system.