LiJiang Extremely High Precision Extrasolar Planets Tracker Instrument On 2.4m Telescope

ABSTRACT We report design, performance from LiJiang Extremely High Precision Extrasolar Planets Tracker Instrument (LiJET) as part of a global network for hunting for low mass planets in the next decade. LiJET is a combination of a thermally compensated monolithic Michelson interferometer and a cross-dispersed echelle spectrograph for extremely high precision Doppler measurements for nearby bright stars (e.g. 1m/s for a V=8 solar type star in 15 min exposure). It has R=18,000 with a 72 micron slit and a simultaneous coverage of 390-694 nm. The commissioning results show that the instrument has already produced a Doppler precision of about 1 m/s for a solar type star with S/N~100 per pixel. The instrument has reached ~4 mK (P-V) temperature stability, ~1 mpsi pressure stability over a week and a total instrument throughput of ~30% at 550 nm from the fiber input to the detector. LiJET also has a direct cross-dispersed echelle spectroscopy mode fed with 50 micron fibers. It has spectral resolution of R=27,000 and a simultaneous wavelength coverage of 390-1000 nm. LiJET is the second instrument, the first same one (EXPERT) was commissioned at the KPNO 2.1m in USA in September 2009 and began its science operation in June 2010. LiJET is scheduled to ship to China for commissioning in December 2010.

Keywords: Extrasolar Planets, Survey, Doppler, Interferometers, Network, Fringing spectra, Radial Velocity, and Fiber-fed

Liang Chang2, Jian Ge4, Yufeng Fan2, Xiaoke Wan4, Bo Zhao4, Peng Jiang1, Scott Fleming4, Yuxin Xin2, Brian Lee4, Suvrath Mahadevan4 Scott Powell4& Frank Varosi4

Wang,Tinggui1 Yuan, Weimin2 Zhou,Jilin3 Ge, Jian4

1, University of Science and Technology of China 2, Yunnan Astronomical Observatory 3, Nanjing University 4,University of FloridaContact e-mail: changliang@ynao.ac.cn

1.INTRUCUCTION

1) LiJET Project Collaborators: USTC, YNAO, NJU, UFL Supported by Chinese Academy of Science and National Science Foundation of China, University of Florida, aNational Science Foundation of USA and also participating institutions including YNAO, USTC, and NJU. 2) Our Design Goals:

☺Use low-cost, compact, robust, low maintenance, but high precision and throughput Doppler instrument; Target bright F,G,K dwarfs (V<8) with slow rotation for detection of super Earth mass planets, including habitable ones; Integrate at least 15 min to minimize RV noises from stellar oscillations for low mass planet detection; A nearly perfect match of ~15 min exposure time requirements and photon noise limit offered by a 2 meter telescope for 0.5-1 m/s; For asteroseismology, only target V<5 stars and ~1 min exposures; Target faint solar type stars up to V~12 for moderate-high Doppler precision measurements; Offer continuous high precision radial velocity measurements for V<8 F,G,K stars with 0.5-1 m/s Doppler precision in 30 min or less; Follow up planet candidates from SDSS-III MARVELS planet survey;

☺Observe other science targets: Stellar spectroscopy, stellar activities, Stellar pulsations and so on.☺Network resources will be available to the entire consortium members;

Spain

SET, 2011?

Fig 1 Global Extremely High Precision Exoplanet Tracker Network

Australia ?

Hawaii ? Chile ?

USA

EXPERT, Sept. 2009

China

LiJET, Dec. 2010

2. INSTRUMENT DESIGN

1) Summary of optical characteristics

Telescope Lijiang 2.4m, F/8

Fiber Input Focal Ratio F/4

Fiber Output Focal Ratio F/4

Slit Size 72um

Main disperser R2 Echelle, 63deg blaze, 87 l/mm

Cross disperser PBM2Y prism, 45 deg apex angle

Collimated beam size 85mm

Detector 4096 x 4096 CCD, 15 micron pixels

Spectra RVM: 390nm-690nm; DEM: 390nm-1000nm

Spectra Resolution RVM: R=18000, DEM: R=27000

Fiber core diameter RVM: 72um; DEM: 50um

4) RVM and DEM Configuration

5) Mechanical and Environment Design

Fig 5 The outside view of the mechanical layout and Top view of LiJET inside. An airtight chamber covers the entire instrument. The dimension for airtight chamber is 30”X30”X65”. The dimension for the thermal enclosure is W50”XL75”XH40”

Fig 6 LiJET instrument in the UF lab

Fig 7 LiJET telescope interface including a fiber feeding system, a fiber tip guiding and a calibration fiber light source. The calibration light was fed from the calibration lamps on the calibration bench inside the instrument control chassis.

3) LiJET Status------Until OCT. 19th, 2010

☺ LiJET already be packed in UF, will ship to China for commissioning in December 2010;☺ LiJET RMS RV errors are close to the required values, <1.5m/s for bright calibration sources in UF lab now.☺ We already built a instrument room for LiJET in 2.4m telescope basement. It’s a temperature and humidity stable room, temperature design goal is ±0.5 ,it have reached ±0.2 ℃ ℃precision in 3 months. And humidity is controlled in 40%-60%.☺ We have prepared all tools and spare parts for LiJET set up and commissioning.

2) Calibration method

Given LiJET is thermally and mechanically very stable over a long period of time, we only use bracketing exposures before and after science images to track local common path changes over the time and subtracting the small drifts during the exposure. We choose the ThAr emission spectra as our primary calibration source and the iodine absorption line spectra as a backup source and also zero offset checking.

3) Pre-slit Optics

RVM and DEM have different pre-slit optics, dispersed interferometric fringe for radial velocity measurement and direct echelle spectra for other sciences.

(a) (b) (c)

Fig 2 LiJET Status. (a) is shown that UF engineers was packing LiJET components; (b) is shown that all parts of LiJET have been packed, it includes Spectrograph main assembly, Temperature-controlled outer enclosure, Damping and support system, Optical alignment system, Electrical, Mechanical Tools and Spare Parts, Cables for spectrograph and LiJET fiber, Telescope interface and guiding system, Control system and calibration device. (c) is shown that the temperature changed followed time, the precision is ±0.2 in 3 months. In ℃Jun.13th 2010,engineer went into ET room for adjust temperature monitor, so the temperature changed large. And from July 21th to 28th,we trued off temperature monitor for building gantry system.

(a) (b)Fig 3 (a) RVM configuration 3-D layout and spectra format on the CCD; (b) DEM configuration 3-D layout and spectra format on the CCD

(a) (b) Fig 4 (a) RVM configuration Solar Spectra on the Detector; (b) DEM configuration cross-dispersed echelle spectra of NSV 860 (K2 EB, V=8.7) in Jan. 2010

R=18,000

***Commissioning Plan, Instrument Testing and Early Science***

☺ ~6 months of commissioning (weather and instrument unpredicted nature and past EXPERT experience), one run/month, ~15 nights/run;☺ First run with three weeks, 1st week, hardware installation, 2nd week integration with the telescope, 3rd week trial observations;☺ Results to meet proposal requirements;☺ Short (<14 days) and long term (~1 yr) RMS precision;☺ Commissioning targets (≥2 RV stable starts, ≥2 RV known planets (one with short period and one with > 1 month period);☺ Early Science: No promise of any science results, but demonstrate its science capability;☺ Commissioning science targets: In Aug. 12th, 2010, the LiJET Project Collaborators discussed detailed commissioning science targets at Hefei City; It includes ~1 m/s science, ~3‐5 m/s science within 6 months and other science targets and plan.