[meteorite-list] Laser Guide Star Adaptive Optics Sharpens Subaru Telescope's Eyesight

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 8 Jul 2011 17:08:34 -0700 (PDT)
Message-ID: <201107090008.p6908YUu010665_at_zagami.jpl.nasa.gov>

http://www.naoj.org/Pressrelease/2011/07/06/index.html

Laser Guide Star Adaptive Optics Sharpens Subaru Telescope's
Eyesight and Opens a New Vision of the Distant Universe

National Astronomical Observatory of Japan
July 6, 2011

A research team at NAOJ has begun scientific observations with Subaru
Telescope's Laser Guide Star Adaptive Optics (LGSAO) system. The LGSAO
uses a powerful laser to illuminate the sodium layer of the atmosphere
and create an artificial guide star that shines in the upper atmosphere
(fig 1 <#1>). The LGSAO system integrates the creation of an artificial
guide star with adaptive optics that compensates for atmospheric
turbulence. This integrated system delivers to the scientific
instruments images that are ten times sharper than previous ones (fig 2
<#2>). Consequently, it will facilitate discoveries of new objects and
clarify the details of other faintly observed ones.

Atmospheric turbulence distorts observations with ground-based
telescopes. The spatial resolution of images from large, 8 - meter
telescopes at the summit of Mauna Kea, known as one of the best sites on
earth for astronomical observations, degrades by a factor of ten. Since
October 2008, Subaru Telescope's adaptive optics system with 188 control
elements (AO188) (Note 1 <#7>) has opened the possibility for the Subaru
Telescope to reach its theoretical capability for high resolution
imaging (Note 2 <#8>). The operation of this powerful system requires
measurement of the atmospheric turbulence toward the target object. By
monitoring the light from a bright star, one can measure how the
turbulent atmosphere distorts the light propagating through it. Such a
bright star used to measure the wavefront aberration of light is called
a "guide star". However, the instrument has only had access to one
percent of all available objects that have sufficiently bright guide
stars for such measurements.

In order to increase the number of targets accessible to AO 188, the
research team (Note 3 <#9>, 4 <#10>) developed an integrated system
(LGSAO, fig 2 <#2>) that combines the Laser Guide Star generation system
with the AO 188 system. The resulting system can generate an artificial
star bright enough to be used as a light source for measuring and
compensating for atmospheric turbulence in any direction where the
Subaru Telescope is pointing (Reference 1 <#13>). The ongoing
performance verification tests have confirmed that the integrated system
performs as designed (fig 3 <#3>).

The LGSAO team started their first scientific observations by targeting
SDSS J1334+3315, a quasar pair discovered by the Sloan Digital Sky
Survey in the constellation Canes Venatici (Note 5 <#11>). This object
consists of two star-like images separated by 0.8 arc seconds and has
been thought to be a double image of a distant quasar gravitationally
lensed by an unidentified foreground galaxy. A gravitational lens is
formed when light from a very distant, bright light source is bent
around a massive object between the source object and the observer,
creating two or more images. The Subaru LGSAO observation of the quasar
clearly revealed the foreground galaxy and demonstrated that its
gravitational lensing effect is responsible for the creation of the
double quasar image (fig 4 <#4>)(Reference 2 <#14>). A short exposure
image (fig 5 <#5>) of another gravitationally lensed quasar system,
B1422+231, also demonstrates the striking improvement in image
resolution when using LGSAO.

The measured redshift distance (i.e., how much the light has been
stretched due to the expansion of the universe) to SDSS J1334+3315
confirms that it is 10.9 billion light years away. The newly discovered
lensing galaxy is likely to be at a distance of 5.4 billion light years
away, based on three independent estimates. Monitoring observations
should confirm the lensing model, which predicts a ten-day time delay
for the source brightness variation between the two lensed images. The
paper reporting these discoveries will be published in the Astrophysical
Journal in July.

Fig. 6 shows a quick look image of the most distant quasar ULAS
J1120+641, that was spotted by UKIDSS survey and confirmed of its
redshift at z=7.085 by Gemini follow-up spectroscopy as reported in the
Nature paper published on 30 June, 2011 (Reference 3 <#15>). NAOJ team
is discussing for possible follow-up observations of this important
object and a test exposure was taken by LGSAO (Note 6 <#12>).

The completion of the Laser Guide Star Adaptive Optics sharpens the
vision of the Subaru Telescope in the near infrared by a factor of ten.
In addition, it opens new prospects for making high-resolution studies
of distant galaxies, quasars, and supernovae, as well as capturing more
detailed images of globular clusters in our Galaxy, for which no nearby
bright natural guide star is available.

The LGSAO system starts its service for open use observations in July
2011. Many researchers from around the world are looking forward to
using this system.



Reference:
1) Hayano et al., SPIE 7736, 21, (2010), "Commissioning status of Subaru
laser guide star adaptive optics system"
2) Rusu et al., in press Astrophys.J (2011), "SDSS J133401.39+331534.3:
A New Subarcsecond Gravitationally Lensed Quasar"
3) Mortlock,D.J. et al., Nature, 474, 616 (2011), A luminous quasar at a
redshift of z=7.085



*Figure 1*: Laser beam shot from the Subaru Telescope to generate an
artificial guide star at a height of 90 km in the upper atmosphere.
(Photo by Daniel Birchall, NAOJ)

*Figure 2*: The Laser Guide Star Adaptive Optics, LGSAO, produces an
artificial guide star at an altitude of 90 km in the upper atmosphere,
bright enough to serve as a light source to measure atmospheric
disturbance, with a wavefront sensor operating at 2000 Hz. A deformable
mirror cancels the wavefront error in real time to improve the spatial
resolution by an order of magnitude.

*Figure 3*: LGSAO observation at the Subaru Telescope control room.

*Figure 4*: Double quasar SDSS J1334+3315 imaged without adaptive optics
(upper left) and with adaptive optics (upper right), each image spanning
a 10 arc second field of view. The lower panel is enlarged by five times
and clearly shows for the first time the lensing galaxy located in
between the two quasar images. Click the image to display the larger
figure. Retrieve the raw image without labels here.

*Figure 5*: Test exposures of the gravitationally lensed quasar
B1422+231 with adaptive optics (right) and without adaptive optics (left).

*Figure 6*: A 10 - minute exposure image of the most distant quasar ULAS
J1120+0641 (lower right), taken by the Subaru Telescope LGSAO at a
wavelength of 2.1 micron. The upper left figure shows the same object
observed with the UKIRT telescope with 40 sec exposure as part of the
UKIDSS sky survey project, also in the near infrared at 2.2 micron.
Field of view is 60 arc seconds. The lower left figure shows a close-up
of 8 arcs second field view, the same as the Subaru Telescope LGSAO
image. Click the image to display the higher resolution image. The raw
image without labels is available through this link. <fig6.jpg>

 

(Note 1) Subaru Telescope Press release: 20 Nov. 2006
<http://subarutelescope.org/Pressrelease/2006/11/20/index.html>

(Note 2) The theoretical limit for the spatial resolution of the Subaru
Telescope, called the diffraction limit, is 0.06 arcsec for infrared
light at 2 microns. At this resolution, one can count the number of golf
balls at the summit of Mt. Fuji from Tokyo, a distance of about 100 km.

(Note 3) Masanori Iye (Project Representative), Hideki Takami, Yutaka
Hayano (Principal Investigator)???Hiroshi Terada, Yosuke Minowa, Masayuki
Hattori, Yoshihiko Saito, Shin Oya, Olivier Guyon, Tae-Soo Pyo, Mai
Shirahata, Makoto Watanabe, Meguru Itoh, Michihiro Takami, Stephen
Colley, Michael Eldred, Mathew Dinkins, Taras Golota, Tom Kane???Vincent
Garrel, Christophe Clergeon.

(Note 4) LGSAO project is supported by MEXT Grant-in-Aid for Specially
Promoted research (2002-2006), "Laser Guide Star Adaptive Optics", and
JSPS Grant-in Aid for Scientific Research (S) (2007-2011) "Laser Guide
Star Adaptive Optics."

(Note 5) Observation team for SDSS J1334+3315 includes Cristian Eduard
Rusu (Univ. Tokyo), Masamune Oguri (IPMU), Issha Kayo (Toho University),
and Naohisa Inada (Nara National College of Technology).

(Note 6) Test observation of ULAS J1120+0641 was made with the
assistance of Chris Simpson (Liverpool Jon Moores University) and
Takatoshi Shibuya (Graduate Univ. for Advanced Studies).
Received on Fri 08 Jul 2011 08:08:34 PM PDT