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We employ high-fidelity Monte Carlo simulations

star sample, illustrating the novelty of the search

as a novel means to design and plan the campaign.

method.

These account for the range in target-star properties (ages, distances, luminosities, masses, and expected

Current Status

AO performance) and allow us to develop robust quantitative metrics for observing: e.g., deeper vs.

On-telescope commissioning of NICI for methane

shallower exposures; more vs. fewer targets; younger,

differential imaging was completed in 2008, with

more distant targets vs. older, closer targets, etc.

the Gemini Observatory staff and campaign team

Perhaps most importantly, the simulations provide a

working closely together to fully test instrument

means to compare the relative value of all potential

operation, develop observing techniques, and assess

targets.

on-sky performance. NICI commissioning data, taken for stars over a wide range in brightness and

The ranking of targets is done by first simulating,

seeing conditions, were used to refine the campaign

for each star, a large number of planets whose

simulations and planning. Overall, though work is

orbits and masses are randomly drawn from the

still ongoing to fully characterize NICI performance,

properties of the known RV-discovered planets,

the instrument appears to perform better than any

and then determining the detectability of these

other existing AO instrument for the detection

simulated planets with respect to the NICI contrast

of faint companions inside a radius of about two

and sensitivity limits, as predicted by substellar

arcseconds.

evolutionary models. While young stars generally tend to be favored, this is not automatically so. In

The first NICI science run was in December 2008,

some cases, older, closer stars are more favorable than

and since then campaign observations have been

more distant, younger stars—the ability to resolve

carried out monthly during bright time around full

the smaller physical separations (where planets are

Moon. Campaign members have gone to Chile to

more likely to reside) can trump the relative gain in

participate in the commissioning and science runs,

contrast from more youthful planets.

and most recently, the team has effectively participated remotely (via videoconferencing, see Figure 2). The

In addition, for the past two years we have carried

Gemini queue system has been a major advantage for

out a search for nearby, young, low-mass stars as

this work, since campaign observations are carried

part of our preparatory effort for the campaign. The

out only during suitable seeing conditions. At other

current young star census in the solar neighborhood

times, regular Gemini queue programs well matched

is mostly restricted to higher-mass (A-, F-, G-, and

to poorer seeing conditions are executed. Following

K-type) stars and contains few M-dwarfs. This

one more science run in April 2009, NICI will be

paucity of M-dwarfs is striking, given that they

removed from the telescope in May for maintenance

dominate the stellar mass function by number, and

and minor upgrades. This is well-timed, since the

is due to the fact that low-mass stars are generally

weather conditions during the Chilean winter are

too faint to be included in the optical catalogs that

typically unsuitable for NICI observing.

have been mined for nearby young stars. To find this “missing” population, we have been searching

The campaign team plans to ultimately observe

for the nearest young M-dwarfs using color selection

about 300 carefully selected stars. As of the end of

and stellar photospheric activity (i.e., “starspots” and

the summer 2009 observing season (which happens

other signs of magnetic stellar “weather”) to identify

in April at Gemini South), about 120 targets have

candidates and pursuing follow-up confirmation

been observed, with the data processed by our team’s

with optical spectroscopy. This M-dwarf search is

pipeline that has been custom-tailored for NICI’s

a key preparatory activity for the NICI campaign

unique datasets. While some potentially interesting

to identify promising targets. Such a sample of

candidates have been found in the initial set of data

objects is also of value for a number of other studies,

(i.e., very faint objects next to the much brighter

including tracing the evolution of circumstellar

science targets), the final confirmation that they are

debris around low-mass stars.

The vast majority

real exoplanets, as opposed to background objects,

of our M-dwarfs are not in any published young-

will come with second epoch follow-up imaging to

June2009

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Issue 38 - June 2009  

GeminiFocus