Deepest yet - Anglo-Australian Observatory

24 Pages·2012·7.66 MB·English

OBSERVER
THE AUSTRALIAN ASTRONOMICAL OBSERVATORY NEWSLETTER NUMBER 121 FEBRUARY 2012
Deepest yet

AAOmega observation
probes dark energy
Starbug Fibre Positioners Time-lapse of the sky over the AAT Tracing the Violent ISM
CONTENTS
SCIENCE HIGHLIGHTS
Using 2dF and AAOmega to Harness the Full Power of the Supernova Legacy Survey 4
Emission Lines in the Near Infrared: Tracing the Violent ISM 6
Dancing Starbugs: vacuum adhesion, field rotation and other progress 8
A message of progress from HERMES 11
Imaging with the 2dF Focal Plane Imager 12
OBSERVATORY NEWS
An Auspicious Launch 13
AusGO CORNER 14
Gemini School Astronomy Image Contest Winner 2011 16
The Sky over the Anglo-Australian Telescope 17
New Faces at the AAO 18
AAO Distinguished Visitors 20
LOCAL NEWS
Epping News 21
Letter from Coona 22
DIRECTOR’S MESSAGE
Director’s message
Matthew Colless
The AAO Forward Look1 is the strategic For the UKST, the science driver is 3. Remote observing and AAT operations
plan setting out the implementation follow-up of the all-sky surveys with model. The AAO aims to phase in remote
framework within which the AAO aims ASKAP and SkyMapper. The AAO will observing on the AAT, so that by 2015 it
to realize the goals and priorities of the examine two potential approaches: a is possible to carry out most standard
Australian Astronomy Decadal Plan 2006- minimal upgrade involving refurbishing observations on the telescope either
2015 and the recent Mid-Term Review of the telescope infrastructure and classically or remotely. The AAO will also
the Decadal Plan2. I have been touring the minor improvements to the existing upgrade the AAT’s infrastructure and
country over the past couple of months 6dF positioner and spectrograph, and instruments, so that by 2015 the daily
visiting all the major centres in order to a maximal upgrade including both burden of repairs and maintenance is
present the draft version of the Forward telescope refurbishment and a new, and reduced by at least 30%.
Look and get feedback from individuals, fully-automated,1000-fibre spectrograph
Remote observing has already been
institutions, and various advisory and positioner. The trade-off between
trialled in a limited way from Epping
committees. This process has been both capital investment and operations costs,
with UCLES, and will be progressively be
valuable and encouraging. Although the as well as the availability of funding, will
implemented for other AAT instruments
plan will benefit from further revision guide the decision of which (if either)
in order of increasing operational
in light of the feedback I’ve received, of these options for the UKST the AAO
complexity. The AAO might initially offer
it’s clear that the general shape of the pursues.
observations from a number of suitably
strategy has strong support from the
2. Review of AAO’s support services equipped remote locations and, in the
community. Consequently, in order to
for large telescopes. The AAO currently longer term, from the astronomer’s
get a head start on some of the major
supports Australian access to large desk or laptop. This offers potential
actions arising from the Forward Look
telescopes through operation of the efficiency savings for users and support
recommendations, I am asking AAO staff
Australian Gemini Office (AusGO), which astronomers, as well as cost savings for
to begin three important and time-critical
includes: managing time allocation on the AAO. Remote observing would be
initiatives in advance of formal completion
Gemini and Magellan through ATAC; at the user’s discretion, and observers
of the Forward Look process.
assisting with proposal preparation, would still be welcome to visit the
1. Development of instrumentation observation planning and data reduction; telescope and work in classical mode;
options for the AAT and UKST. The providing travel support for observers; the AAO will continue to provide support
Forward Look concludes that high taking part in public relations and for visiting observers’ travel and living
priority should be given to another major outreach activities; and participating in expenses.
instrument for the AAT (see p28, priority instrumentation projects.
Although the AAT manages to keep
#1) and that it is also desirable, if funding
The AAO will to carry out a review of the downtime due to technical problems
can be found, to upgrade the UKST
functions and structure of the AusGO below 3%, this high level of reliability is
telescope and provide it with a new multi-
during 2012 in order to determine the presently achieved by continual technical
object spectrograph and positioner system
most effective ways in which it can intervention and support. Improving
(see p28, priority #4).
add value to Australian astronomers’ the reliability of the infrastructure
For the AAT, the process of identifying the access to Gemini and other offshore and instruments through a program
best new instrument will follow the iterative large telescopes. The AusGO has been of upgrades and enhancements can
consultative approach successfully used to highly effective in the management of substantially reduce the required
select HERMES in 2008. That is, the AAO Australia’s participation in Gemini and level of daily support and repairs, and
will outline a handful of strawman concepts Magellan, but it is difficult to determine free technical staff at the telescope
and put these cases, designs and costs to how much value it is adding to users’ for strategic project work on new
the community for consideration. These observing experience. The AAO is instruments or other telescope
concepts will be weighed and sifted through prepared to re-structure the AusGO improvements.
a workshop process that will eliminate and potentially provide it with greater
These are just the first three major
some concepts and perhaps propose resources in order to enhance the service
initiatives from the Forward Look. The
others. The AAO will develop this revised set it provides. To this end the AAO needs
plan contains many other improvements,
of concepts to the level of costed feasibility to consult with the user community
both major and minor, that the AAO
studies and then ask the community and determine what mix of services the
intends to implement over the next
to evaluate the options and come to a AusGO could provide that would improve
few years. I encourage you to read
consensus recommendation for the next the research outcomes from access to
the Forward Look and see what other
major AAT instrument. The AAO aims to large telescopes.
enhancements to our facilities and
carry out this process during 2012, noting
services we will be introducing.
that HERMES will be commissioned in the
first half of 2013.
1 www.aao.gov.au/AAOForwardLook.html
2 w ww.science.org.au/natcoms/nc-astronomy/decadalplan.html
SCIENCE HIGHLIGHTS
Using 2dF and AAOmega to Harness the Full Power
of the Supernova Legacy Survey
Chris Lidman, (AAO and CAASTRO1), Vanina Ruhlmann-Kleider (DSM/IRFU/SPP, CEA-Saclay, France) and
Karl Glazebrook (Swinburne University and CAASTRO)
The Nobel Prize winning discovery of1 Using AAOmega and 2dF to test a and more distant ones) can be found.
the accelerating Universe [1,2] was new approach This has been done in [5]. From the first
made from observations of a few dozen 3 years of SNLS data, [5] find about 400
An alternative yet unproven approach
distant Type Ia supernovae (SNe Ia). The SNe of all types per SNLS field. Only
to classifying SNe (and obtaining their
reason for the acceleration is arguably about a third of these have a redshift.
redshifts) from real-time spectroscopy
the biggest unsolved mystery in physics.
is to classify SNe using multi-colour Each SNLS field covers 1 square degree,
Possible explanations range from
lightcurves and to obtain the redshifts so both the number density of supernova
vacuum energy to modifications to the
of the host galaxies after the SNe have hosts and the area they covered were
theory of General Relativity.
faded from view. The principle advantages well matched to the capabilities of the
Mapping out in greater detail the of this technique are i) host galaxy 2dF positioner (400 fibres over a 2 degree
expansion history of the Universe is the redshifts can be taken at any time, and diameter field). The median r-band
aim of current SN Ia surveys, as this ii) it usually takes much less time to magnitude of the hosts is 23, which is
may offer clues as to what causes the measure the redshift of a galaxy than to considerably fainter than what is usually
Universe to accelerate. Currently, the spectroscopically confirm a SN Ia. attempted with AAOmega. Exposure
largest published individual sample of times were therefore long, up to 60,000
In order to test this approach, we recently
distant supernovae is the 3-year sample seconds. The two SNLS fields were
observed two of the four SNLS fields
from the Supernova Legacy Survey observed during 4 clear nights during
(D1 and D4) with the 2dF fibre positioner
(SNLS), which contains 252 supernovae August 2011.
and AAOmega. All 252 SNe Ia in the
extending out z=1.06 [3].
SNLS 3-year sample were discovered in Histograms showing the number of
All the supernovae in the SNLS “real-time”, which meant that only part objects that were targeted and the
3-year sample were spectroscopically of the lightcurve (usually the rising part) number of objects for which a redshift
confirmed. Confirming a Type Ia was used to find SNe Ia. Now that the was obtained are shown in Fig. 1. In
supernova (SN Ia) at z 0.7 from its SNLS survey has been completed, it is total, redshifts were obtained for 398
spectral features typically takes about possible to use the entire data set to find host galaxies. The completeness fraction
an hour of integration w~ith an efficient supernovae. Since the entire lightcurve is is 60%. Most of the galaxies that lack
spectrograph on an 8m class telescope. used, more supernovae (especially fainter redshifts are fainter than r=23.
The SNe Ia are observed one at a time, as
is it very rare to have more than one SN
Figure 1: Histograms of the
Ia visible within one week of maximum
HoststargetedwithAAOmega
number of objects plotted as a
light at any given time within the fields of 100 HostredshiftsfromAAOmega function of magnitude (above)
view that are available with the current SecurehostredshiftsfromAAOmega
and redshift (below). The blue,
generation of spectrographs on 8m class
80 Medianmagnitudes:23.18,22.33and21.93 green and tan histograms
telescopes. Usually, SNe Ia have to be
represent all objects targeted
observed within one week of maximum
60
with AAOmega, all objects with
light, otherwise they are too faint. The
secure AAOmega redshifts
observations are, therefore, also time-
40
(two or more clearly identified
critical.
spectral features), and all
This means that many hundreds of hours 20 objects with either a secure
of time-critical 8m telescope time were AAOmega redshift or a probable
required to spectroscopically confirm all 0 16 18 20 22 24 26 28 30 one. If the r-band magnitude of
r(AB)
252 SNe Ia in the SNLS 3-year sample. the host was unavailable, then
Future surveys, such as the supernova Hostswitharedshift(spec.orphoto.) the object was not plotted in the
survey of the Dark Energy Survey (DES) 60 HostredshiftsfromAAOmega upper plot. If a spectroscopic
[4], will be an order of magnitude larger SecurehostredshiftsfromAAOmega redshift is not available for
than SNLS. It therefore seems unlikely 50 Medianredshifts0.70,0.62and0.56 the lower plot, we use the
that these surveys will be able to 40 photometric one. If neither a
spectroscopically confirm all the SNe Ia spectroscopic nor a photometric
that they will discover. 30 redshift were available, then
the object was not plotted. The
20
median magnitude and redshifts
of objects in the blue, tan and
10
green histograms annotate
1 CAASTRO – ARC Centre of Excellence for All-sky 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 each figure.
redshift
Astrophysics
4 Australian Astronomical Observatory Newsletter - FEBRUARY 2012
SCIENCE HIGHLIGHTS
Summary and Future Work
We have demonstrated that we can use
50 FORS1+2 median redshift 0.59 2dF and AAOmega to obtain redshifts for
large numbers of galaxies that hosted
40 AAOmega median redshift 0.62
photometrically classified SNe Ia. The
30 approach is a promising alternative to
obtaining a spectrum of every supernova
20 — one at a time — while it is still bright
enough to do so. However, before such
10
samples can be used to constrain
0 cosmology, the biases in them need to be
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
examined.
redshift
100 An example of a bias is the relative
FORS1+2 median R mag 22.06 ease at which redshifts can be obtained
80 for galaxies that are actively forming
AAOmega median R mag 22.23
stars compared to galaxies that don’t. If
60
there were no correlation between the
properties of SNe Ia and their hosts, then
40
this would not cause a bias. However,
there is ample evidence for such
20
correlations. For example, SNe Ia in star-
forming galaxies tend to have broader
0
16 18 20 22 24 26 light curves [6], which means that they
r(AB) are also brighter. By preferentially
obtaining redshifts for star-forming
Figure 2: A comparison of the host redshift and magnitude distributions obtained
hosts, one is also preferentially selecting
with FORS1 and FORS2 and AAOmega.
brighter supernova. Uncorrected,
this bias might be large enough
to significantly change the derived
cosmology.
Our observations of the SNLS fields
The median redshift of galaxies with a The redshifts from FORS1 and FORS2 with AAOmega allow us to examine the
redshift from AAOmega is similar to the came from 66 separate MOS setups. effect that this and other biases have
median redshift of SNe Ia in the 3-year Summed over all setups, the total on the cosmological results, since we
SNLS survey. It is also similar to the amount of time spent with FORS1 can compare the cosmology that was
median redshift of SNe Ia that will be and FORS2 was 240,000 seconds. For derived for the 3 year SNLS sample with
found in the supernova survey of DES [4]. AAOmega, the integration time totalled the cosmology that is derived from the
92,500 seconds. sample that uses host galaxy redshifts.
A comparison between FORS on The results of this work will have an
At face value, it would seem that
the VLT and AAOmega important bearing on how redshifts are
AAOmega — a multi-object spectrograph
obtained for future SN surveys, such as
It is instructive to compare the results on a 4-metre class telescope - has
the SN survey of DES.
we obtain here with the results that resulted in many more redshifts than
we obtained with FORS1 and FORS2 FORS1 and FORS2 — both multi- [1] Riess, A. G. et al. 1998, AJ, 116, 1009
during the real time follow-up of live object spectrographs on 8-metre class [2] Perlmutter, S. et al. 1999, ApJ, 517, 565
candidates. During the final two years of telescopes. While this is true, the [3] Guy, J. et al. 2010, A&A, 523, A7
the spectroscopic follow-up of candidates difference is not as extreme as that [4] Bernstein, J. P. ArXiv preprints
with the VLT, the MOS mode of FORS1 suggested by inspecting Figure 2, since [5] Bazin, G. et al. 2011, A&A, 534, A43
and FORS2 was used to observe both live the number of targets available for the [6] Sullivan, M. et al. 2006, ApJ, 648, 868
candidates and the host galaxies of other AAOmega follow-up was about a factor of
transients that were discovered in earlier two larger than the number available for
years. By the end of the SNLS survey, FORS1 and FORS2. The main reason for
there were typically three to four host the difference comes from the difference
galaxies visible in the FORS 7 x 7 FoV. in the field of view between AAOmega and
FORS2. With AAOmega, one can cover
In Figure 2, we compare, the magnitude
’ ’
the entire 1 sq. degree SNLS field in one
and redshift distributions of objects
shot, which is 60 times the area that can
that were observed with FORS1 and
be covered by FORS2. This more than
FORS2 with those that were observed
compensates for differences in telescope
with AAOmega. Excluding any sort
aperture and image quality.
of renormalisation to account for
differences in exposure times, observing
efficiency, and target selection, the
redshift distributions are broadly similar.
Australian Astronomical Observatory Newsletter - FEBRUARY 2012 5
SCIENCE HIGHLIGHTS
Emission Lines in the Near Infrared: Tracing the
Violent ISM
Jae-Joon Lee1, Bon-Chul Koo2 and the GEMS03 team
The AAO looks for opportunities to exploit its infrared is visible from the ground with of the jets and outflows in star-forming
facilities in ways that will provide valuable the high spatial or spectral resolution regions provide estimates on essential
outcomes for the Australian astronomical critical to probing the kinematics of gas. parameters of star formation (e.g. star
community. This includes swapping formation efficiency) and shed light on
The prominent emission lines from
AAT time in exchange for time on other the physics of cloud collapse and star
the ISM in the near infrared are atomic
telescopes and selling AAT time in order formation in giant molecular clouds.
hydrogen (e.g. Br γ) and molecular
to invest in new capabilities (generally Individually, jets and outflows pin-point
hydrogen (e.g., H 2.12 μm). Singly-ionized
new instrumentation). In December 2010 2 the locations of protostars, helping us
Iron emission lines (e.g. [Fe II] 1.64 μm) are
the AAO agreed to sell 15 AAT nights in to understand the formation of stars
also important. In particular, H lines and
Semester 2011A to the Korean Astronomy 2 (Figure 1).
[Fe II] lines trace the dense molecular and
and Space Science Institute (KASI), with
atomic gas associated with massive stars. Feedback from massive stars is a critical
the revenue being used to develop new and
ingredient of the galactic environment.
upgraded AAT instruments. These nights
H and [Fe II] emission lines as One key to understanding the evolution
were allocated to a KASI program using 2
probes of violent ISM around of massive stars and their subsequent
IRIS-2 to obtain near-infrared imaging and
Stars feedback to their environment is mass
multi-slit spectroscopy of the interstellar
medium around star-forming regions. The Jets and outflows signify star formation. loss. Circumstellar shells serve as a
following article reports on this research. H and [Fe II] emission lines probe fossil record of the mass loss history of
2
these jets and outflows effectively (Bally the central, evolved stars. [Fe II] and H
2
Stars are closely linked to the inter- et al., 2007). Both species produce a lines have been detected from shells
stellar medium (ISM) around them. Stars wealth of lines across the near infrared, around some evolved massive stars,
form from the ISM and greatly influence allowing us to measure the excitation and such as luminous blue variables (LBVs),
it throughout their lifetimes and as they kinematics of gas. Collective properties and are effective probes of their eruptive
expire. Jets and outflows from protostars,
UV radiation and mass-loss from evolved
stars and supernova all heat and excite
the ISM and drive turbulent motions
within the ISM. Massive stars and novae
enhance metal abundances in the ISM,
dominating the chemical evolution of
Universe. Because these processes are
so closely linked, the formation and
evolution of stars, particularly massive
ones, must be understood in the context
of their interaction with the ISM. 123
Emission lines from the interstellar gas
trace the violent interaction between
stars and ISM. The Hα (6563Å) emission
line has been widely used in this regards,
and it typically traces diffuse ionized gas.
However, due to interstellar extinction,
the Hd emission line can only probe
relatively nearby regions in our Galaxy.
The interstellar extinction problem is
worse for the ISM around massive stars
because these regions are often distant
and obscured by large columns of gas.
Infrared observations suffer less from
extinction, and therefore are better
suited to studying the ISM near massive
stars. Although deeper observations
are possible in the far infrared, the near Figure 1. A colour-composite image showing the remarkable massive star forming
region G35.2N. The prominent H outflow with associated [Fe II] knots is clearly
1 Korea Astronomy and Space Science Institute, Korea. visible. Red: H 2.12 μm, Green: [2F e II] 1.64 μm, Blue: H band. The H and [Fe II]
Email : [email protected] 2
2 Seoul National University, Korea images are taken with IRIS2. The H image is from the UWISH2 survey.
2
3 Galaxy Ecology and Massive Stars at z=0
6 Australian Astronomical Observatory Newsletter - FEBRUARY 2012
SCIENCE HIGHLIGHTS
mass-loss. These emission lines are also
found in post-AGB stars and planetary
nebulae. They also trace the interaction
of supernova remnants with dense
interstellar and circumstellar gas well.
[Fe II] emission from young core-collapse
supernova remnants (SNRs) can provide
detailed information on the distribution,
dynamics, and chemistry of iron-rich
ejecta material. And, the expanding
supernova shock waves serve as a time
machine to probe the mass loss history of
the progenitors, by interacting with dense
interstellar clouds or pre-existing dense
circumstellar structures and emitting in
the near infrared.
IRIS2 Observations of [Fe II]
emission from young core-
collapse Supernova remnants
Using IRIS2 on the AAT, our group has
been observing star-forming regions,
evolved massive stars and supernova
remnants. Here we briefly summarize
our preliminary results on the near
infrared observations of young core-
collapse supernova remnants.
Near infrared observations are useful for
studies of circumstellar gas in supernova Figure 2. A colour-composite image showing the Galactic supernova remnant RCW
remnants. Of particular interest are 103. Red: H , Green: [Fe II] 1.64 μm, Blue: J band. The H and [Fe II] images are
cont cont
young core collapse SNRs with central taken with IRIS2. The J band image is from the 2MASS survey.
compact objects and a bright X-ray (of
normal abundances) and/or far infrared
shell. A good example is G11.2−0.3, with
indicate complicated mass loss history survey is the UKIRT Widefield Infrared
A 13 mag. We discovered long, clumpy
V of progenitor stars. The circumstellar Survey for H (UWISH2; Froebrich et al.,
[Fe II] and H filaments which we believe 2
2 structure may arise from the interaction 2011). This survey covered 150 square
ar~e emission from dense presupernova
of fast winds of Wolf-Rayet stars with degrees along the Galactic Plane
circumstellar wind shocked by a SNR
slow, dense winds from a prior red (10° l 65°; -1° b +1°) with WFCAM at
blastwave (Koo et al., 2007). We also
supergiant phase, or it may arise from UKIRT to detect the molecular hydrogen
discovered faint, knotty features in the
episodic mass loss associated with 1-0 S<(1)< emission< lin<e at 2.12 μm and
interior of the remnant, which turn out to
interacting binary stars or luminous blue probe a dynamically active component of
be dense ( 103 cm-3) iron ejecta (Moon et
variables. We expect our ongoing studies star formation not covered by broad-band
al., 2009).
of these SNRs could provide constraints surveys. Our group is planning a similar
~
Using IRIS2, we carried out near infrared on the pre-supernova mass loss history unbiased survey using WFCAM at UKIRT
narrowband imaging and spectroscopic of massive stars. Additionally, we with a narrowband filter centered at
observations of several young core- searched for faint [Fe II] emission knots [Fe II] 1.64 μm. We hope our survey, once
collapse SNRs in the southern sky. Our with high radial velocities, which could be completed, will complement the UWISH2
preliminary results show that [Fe II] candidates for fast moving ejecta in young survey and other broadband surveys to
emission is rather common among core-collapse SNRs. We have detected enable a better understanding of our
those SNRs, showing bright filaments [Fe II] knots showing velocities of several Galaxy and provide the community with a
and knots (Figure 2). The measured hundred km/s, and we are investigating legacy dataset useful for a wide variety of
radial velocities of these bright [Fe II] the origin of these features. astrophysical investigations.
features suggest the emission is not
from fast-moving ejecta of the progenitor A Near Infrared Narrowband References
stars but more likely from circumstellar Wide-field Imaging Survey Bally et al. 2007, Protostars and Planets V, 215
matter. X-ray emission associated Our own Galaxy and its inner workings of Froebrich et al. 2011, MNRAS, 413, 480
with these [Fe II] emission features star birth and death are still mysterious. Koo et al. 2007, ApJ, 657, 308
also shows no sign of enhanced metal Unbiased imaging surveys of the Galactic Moon et al. 2009, ApJL, 703, 81
abundances. These observations lead plane in broadband infrared, such as
us to speculate that the [Fe II] emission Glimpse and MIPSGAL, have greatly
is from dense circumstellar structures increased our understanding of our
that existed before the supernova Galaxy. A narrowband imaging survey
explosion, which later become shocked can complement broadband surveys by
by the supernova blast waves. And these focusing on emission line objects. An
pre-exisiting circumstellar structures excellent example of such a narrowband
Australian Astronomical Observatory Newsletter - FEBRUARY 2012 7
SCIENCE HIGHLIGHTS
Dancing Starbugs: vacuum adhesion, field rotation
and other progress
James Gilbert, Jeroen Heijmans, Michael Goodwin, Stan Miziarski, Rolf Muller, Will Saunders, Alex Bennet,
Julia Tims (AAO)
The past year, 2011, was a productive with ability to operate over large focal Defying gravity
year for the Starbug fibre positioner planes. A Starbug prototype is shown
Early Starbug prototypes for MANIFEST
concept. In fact it hardly seems fair to call in Figure 1. Their simple design
used a pair of magnets to clamp each
it a concept these days. Driven principally incorporates two piezoceramic tubes to
Bug to the field plate (see Figure 4).
by the proposed Many Instrument Fibre form a pair of concentric ‘legs’ which, with
This necessitated a very low friction
System (MANIFEST) facility for the Giant the application of specific waveforms,
coating on the top side of the plate so
Magellan Telescope, Starbugs are now can produce a micro-stepping motion in
that the Starbugs could drag along their
performing better than ever. ±x and ±y directions. The robots have a
respective ‘slave magnets’. Not only
clear central aperture for the insertion of
Starbugs are miniature ‘walking’ robots was it difficult to source a sufficiently
fibre bundles or fore optics (see Figure 2).
developed to overcome the limitations of wide-band coating with a very low
For the MANIFEST design, the Starbugs
sequential ‘pick and place’ positioners friction coefficient, but also the Starbugs
hang upside down beneath a curved glass
by moving many optical payloads struggled to tow this heavy magnetic
field plate (see Figure 3). This eliminates
simultaneously. Starbugs provide fast ‘ball and chain’ around, especially up an
the need for fibre retractors, but also
field configurations of several minutes inclined field plate. A recent advancement
presents a number of new challenges.
has eliminated many of these problems:
a vacuum is now used to adhere Starbugs
to the field plate, with a thin silicone hose
(cid:17)(cid:1)(cid:11)(cid:4)(cid:3)(cid:13) connecting each Bug to an evacuated
(cid:18)(cid:19)(cid:12)(cid:10)(cid:10)(cid:14) reservoir (see Figure 5). The removal
(cid:1)(cid:2)(cid:2)(cid:3)(cid:4)(cid:5)
(cid:6)(cid:1)(cid:3)(cid:7)(cid:8) (cid:6)(cid:8)(cid:4)(cid:9) of the magnet assembly has resulted
(cid:9)(cid:10)(cid:11)(cid:3) in major improvements to Starbug
performance, as well as a reduction of
(cid:8)(cid:10)(cid:9)(cid:3)(cid:4)(cid:5) their overall diameter and therefore their
(cid:6)(cid:1)(cid:3)(cid:7)(cid:8)
minimum spacing. These advantages
(cid:9)(cid:10)(cid:11)(cid:3)
(cid:8)(cid:6)(cid:9)(cid:1)(cid:12)(cid:13)(cid:5) have so far outshone the disadvantages
(cid:14)(cid:8)(cid:15)(cid:10)(cid:16)(cid:3)
of using an active vacuum system.
Figure 2: Drawing showing a section
view of the current generation Starbug
Figure 1: A recent Starbug prototype; design; the central tube is kept clear for
ruler graduations are in millimetres insertion of a cylindrical optics ‘module’
(cid:11)(cid:18)(cid:2)(cid:9)(cid:16)(cid:5)(cid:4)(cid:1)(cid:18)
(cid:12)(cid:13)(cid:9)(cid:14)(cid:10)(cid:15)(cid:6)(cid:4)(cid:16)(cid:2)(cid:11)(cid:11)(cid:6)
(cid:7)(cid:5)(cid:10)(cid:16)(cid:15)(cid:6)(cid:17)(cid:16)(cid:2)(cid:18)(cid:10)
(cid:11)(cid:18)(cid:2)(cid:9)(cid:8)(cid:13)(cid:4)(cid:11)
(cid:1)(cid:2)(cid:3)(cid:4)(cid:5)(cid:3)(cid:4)(cid:6)
(cid:7)(cid:5)(cid:8)(cid:9)(cid:10)(cid:11)
Figure 4: Early Starbug prototypes for
Figure 3: MANIFEST has Starbugs walking on the underside of a curved glass field MANIFEST used a pair of magnets to
plate; drawing not to scale clamp them to the glass field plate
8 Australian Astronomical Observatory Newsletter - FEBRUARY 2012
SCIENCE HIGHLIGHTS
Figure 6: The Starbugs ‘test rig’ has
control electronics and metrology for
up to 20 Starbugs; in the centre of
Figure 5: A demonstration of the new vacuum adhesion method, showing a single
the enclosure is an interchangeable
Starbug on a vertical glass surface
400 mm diameter glass field plate
Field rotation positional feedback for control software Figure 7 shows the relationship between
running on a desktop PC. The entire waveform frequency and Starbug speed.
An important breakthrough in the past
system is mounted on a motor-driven There is a clear linear range up to 150 Hz.
months has been the implementation
axle to simulate the movement of a Frequencies up to 300 Hz, though more
of a rotation mode for Starbugs. The
telescope from zenith to the horizon. prone to perturbations, yield speeds
fundamental design of the ‘discrete
approaching 5 mm/s and can be effective
stepping Starbug’ had only ever Starbugs require four waveforms to
when covering large distances. Over
accommodated translation in ±x and ±y operate, which have a specific shape in
time, a nominal waveform frequency of
directions, but the invention of a new order to produce the discrete stepping
100 Hz has been empirically established
sequence of actuator movements has now motion. A Bug’s direction of movement
as a balance of speed, accuracy and low
added angular positioning to the mini- is set by applying these waveforms to
power consumption. Figure 8 shows how
robots’ repertoire. Preliminary testing has different electrodes on the piezo actuators.
very fine positioning can be achieved by
shown that this technique is reliable and The step size and movement speed of a
lowering the Starbug’s drive voltage and
repeatable, with angular speeds in excess Starbug can be controlled by changing the
reducing its step size.
of 55 deg/s under nominal operation amplitude and frequency of the waveforms.
and a minimum angular step size of
approximately 4 arcmins.
The freedom to arbitrarily rotate individual (cid:3)(cid:2)(cid:3)
Starbugs brings new possibilities for the
(cid:3)(cid:2)(cid:1)
positioning system: optimised routing
(cid:7)(cid:2)(cid:3)
and collision avoidance with lower
reconfiguration times; precise angular (cid:7)(cid:2)(cid:1)
placement of non-symmetric optical (cid:6)(cid:2)(cid:3)
payloads (e.g. alignment of IFUs); and (cid:17)(cid:18)(cid:19)(cid:13) (cid:6)(cid:2)(cid:1)
field rotation compensation and tracking (cid:17)
during observations. (cid:3)(cid:16)(cid:9)(cid:10) (cid:5)(cid:2)(cid:3)
(cid:3) (cid:5)(cid:2)(cid:1)
(cid:15)
(cid:14)
Performance data (cid:4)(cid:2)(cid:3)
(cid:8)(cid:9)(cid:10)(cid:11)(cid:12)(cid:13)(cid:9)(cid:14)
Baseline performance data for the (cid:4)(cid:2)(cid:1) (cid:15)(cid:16)(cid:17)(cid:9)(cid:10)(cid:13)
current vacuum Starbug design has been (cid:1)(cid:2)(cid:3)
obtained using a dedicated laboratory (cid:1)(cid:2)(cid:1)
‘test rig’, shown in Figure 6. The test (cid:1) (cid:3)(cid:1) (cid:4)(cid:1)(cid:1) (cid:4)(cid:3)(cid:1) (cid:5)(cid:1)(cid:1) (cid:5)(cid:3)(cid:1) (cid:6)(cid:1)(cid:1)
rig has control electronics for up to 20 (cid:1)(cid:2)(cid:3)(cid:4)(cid:5)(cid:3)(cid:6)(cid:7)(cid:8)(cid:9)(cid:10)(cid:11)(cid:12)(cid:13)
Starbug devices and a 400 mm diameter
interchangeable glass field plate. A high Figure 7: Plot of Starbug speed vs. waveform frequency; speed increase is linear to
resolution machine vision camera is approx. 150 Hz
mounted above the plate and provides
Australian Astronomical Observatory Newsletter - FEBRUARY 2012 9
SCIENCE HIGHLIGHTS
Figure 9 shows that tilting the field plate
Starbug vital statistics
through 90 degrees results in a small
and approximately linear decrease in
performance. These results are for a
Key performance figures for the current „ Maximum speed at 90 degree tilt:
0.5 m long bundle of seven copper
Starbug design for MANIFEST: 4.0 mm/s
wires, four optical fibres and a silicone
~vacuum hose hanging from the Starbug. „ Degrees of freedom: x, y, θ „ >Nominal speed at zenith: 2.1 mm/s
Minimum separation „ Minimum x-y step size: 1 μm „ Nominal speed at 90 degree tilt:
1.8 mm/s
The current generation of Starbugs for „ Minimum angular step s<ize:
MANIFEST have a diameter of 8 mm, 4.1 arcmin „ Minimum separation (pitch): 10 mm
which, with a space cushion, gives a
„ Maximum angular speed: 55 deg/s „ Mass without wiring/hose: 3.5 g
~
minimum separation of ~10 mm. This
sizing produces a good holding force (due „ Maximum speed at zenith:> „ Mass with wiring/hose: 5.6 g
to the area under vacuum) and meets 4.5 mm/s
the target performance figures for the
>
MANIFEST positioner. Previous prototype
Starbugs as small as 6.3 mm in diameter
have performed adequately; Starbugs
(cid:3)(cid:4)(cid:2)(cid:1)
smaller than this are a possibility, although
at a cost of speed and payload size. (cid:3)(cid:3)(cid:2)(cid:1)
(cid:3)(cid:1)(cid:2)(cid:1)
Current work (cid:7)(cid:6)(cid:2)(cid:1)
At the time of writing we are close (cid:16)(cid:13) (cid:7)(cid:5)(cid:2)(cid:1)
to completing the first parallel (cid:7)(cid:22) (cid:7)(cid:4)(cid:2)(cid:1)
(cid:20)(cid:21)
positioning test of 10 vacuum type (cid:19)(cid:17) (cid:7)(cid:3)(cid:2)(cid:1)
Starbugs. A similar test was conducted (cid:2)(cid:5)(cid:11) (cid:7)(cid:1)(cid:2)(cid:1)
(cid:18)
with the old magnetic type Bugs in (cid:15)(cid:5)(cid:16)(cid:17) (cid:6)(cid:2)(cid:1)
March 2011. We expect significant (cid:14)(cid:9)(cid:2) (cid:5)(cid:2)(cid:1) (cid:8)(cid:9)(cid:10)(cid:11)(cid:12)(cid:13)(cid:9)(cid:14)
performance improvements with the
(cid:4)(cid:2)(cid:1) (cid:15)(cid:16)(cid:17)(cid:9)(cid:10)(cid:13)
new demonstration, especially at large
(cid:3)(cid:2)(cid:1)
field plate angles. This task has been
(cid:1)(cid:2)(cid:1)
undertaken by AAO summer student Alex
(cid:1) (cid:4)(cid:1) (cid:6)(cid:1) (cid:7)(cid:3)(cid:1) (cid:7)(cid:5)(cid:1) (cid:3)(cid:1)(cid:1) (cid:3)(cid:4)(cid:1)
Bennet. Alex is also assisting Michael
(cid:1)(cid:2)(cid:3)(cid:4)(cid:5)(cid:6)(cid:7)(cid:8)(cid:9)(cid:3)(cid:10)(cid:2)(cid:5)(cid:11)(cid:12)(cid:13)
Goodwin with earthquake simulation
tests on the Starbug/vacuum system.
Figure 8: Plot of Starbug step size vs. waveform amplitude; results show an
expected linear relationship
Future work
Planned work for the near future will
encompass further development of the (cid:3)(cid:2)(cid:4)
MANIFEST Starbugs system and Starbug (cid:3)(cid:2)(cid:3)
technology as a whole. Tasks will include:
(cid:3)(cid:2)(cid:1)
„ Lifetime wear tests: simulation of a (cid:7)(cid:2)(cid:6)
Starbug’s mechanical wear over the (cid:7)(cid:2)(cid:5)
life of an instrument (cid:17)(cid:13) (cid:7)(cid:2)(cid:4)
(cid:15)(cid:16)
„ Temperature effect tests: analysis (cid:15) (cid:7)(cid:2)(cid:3)
of ambient temperature effects on (cid:3)(cid:5)(cid:6)(cid:12) (cid:7)(cid:2)(cid:1)
(cid:3)
Starbug performance (cid:7) (cid:1)(cid:2)(cid:6)
(cid:14)
(cid:1)(cid:2)(cid:5)
„ Field plate optical coating tests: (cid:12)(cid:13)(cid:14)(cid:15)(cid:16)(cid:17)(cid:13)(cid:18)
measuring scratch/dig after long (cid:1)(cid:2)(cid:4) (cid:19)(cid:20)(cid:21)(cid:13)(cid:14)(cid:17)
term use (cid:1)(cid:2)(cid:3)
(cid:1)(cid:2)(cid:1)
„ New Starbug designs: testing of
(cid:1) (cid:7)(cid:1) (cid:3)(cid:1) (cid:8)(cid:1) (cid:4)(cid:1) (cid:9)(cid:1) (cid:5)(cid:1) (cid:10)(cid:1) (cid:6)(cid:1) (cid:11)(cid:1)
larger Starbug variants for moving (cid:1)(cid:2)(cid:3)(cid:4)(cid:5)(cid:6)(cid:7)(cid:4)(cid:8)(cid:9)(cid:3)(cid:6)(cid:8)(cid:10)(cid:11)(cid:4)(cid:3)(cid:6)(cid:12)(cid:5)(cid:3)(cid:11)(cid:13)
large fibre bundles / IFUs
Figure 9: Plot of nominal Starbug speed vs. field plate angle for a 0.5 m long fibre/
„ Pick-off mirror integration:
wire bundle
investigation of Starbugs’ suitability
~
for pick-off mirror systems
„ Optimisation of electronics: reduction
of the control system’s size, cost,
power and heat dissipation
10 Australian Astronomical Observatory Newsletter - FEBRUARY 2012