You will be presented with the full text of a science research paper. Please write an abstract for this paper. Your response should include the abstract and no additional text.

Paper text:
the study of exoplanetary systems is arguably the most rapidly developing field in modern astrophysics .
surprisingly , much progress has been made without directly imaging a single planet : radial velocity / microlensing and primary and secondary planet eclipses provide limited , but valuable insights .
direct imaging of planetary systems will have a fundamental impact on the field  a single , low 
resolution 35 @xmath4 m spectrum of a planet may carry more information than all existing spitzer transit photometry combined . as was the case in the search for the first brown dwarf , or for radial velocity and planet transit techniques , achieving the first firm detection is a very difficult and often frustrating challenge .
but these investments paid off rapidly by opening whole new classes of objects for study .
using rotational subtraction of the persistent speckle pattern and the image artifacts , adaptive optics systems are capable of reaching very high contrast .
low thermal  background telescopes , such as very large telescope ( vlt ) and the multiple mirror telescope ( mmt ) , can utilize this technique in the l  band where the superior adaptive optics  correction ( strehl ratios 80%90% vs. 3045% in h  band ) further increases the contrast .
our recent vlt / naco l  band observations routinely achieved @xmath5l=11 mag contrast at 1 " and larger separations .
this contrast , in combination with the typical color of older planets ( h@xmath6l=5.5 mag , 2 gyr , 5 m@xmath7 , @xcite ) , provides more than 1  mag sensitivity increase over spectral differential imaging @xcite .
using the l  band angular differential imaging technique on the vlt / naco we carried out a survey of 21 young stars , members of the nearby tucana  horologium ( 1030 myr ) and the @xmath0 pictoris moving groups ( @xmath812 myr ) .
no substellar companions were found around the target stars , but the companion to 51 eri , gj 3305 , was found to be a very close binary on an eccentric orbit .
our sensitivity would have allowed the detection of companions as small as a jupiter mass at orbital distances typically of 5 au .
the absence of detected companions sets constraints on the frequency and maximum orbital distance of giant exoplanets .
we show that a radial distribution of planetary companion with a maximum orbital radius exceeding 30 au  in combination with a power  law index of 0.2  can be rejected at a 90% confidence level ( see , fig . 1 and @xcite ) .
this demonstrates that giant planets are relatively rare at large separations .
a similar conclusion was reached subsequently by other independent surveys ( e.g. @xcite ) .
the result of our naco survey also offers an explanation of why most current and past direct imaging surveys failed to detect a giant planet population : most of these focus on near  infrared wavelengths ( 12.2 @xmath4 m ) , representing a trade  off between the rise of the thermal background toward the longer wavelengths and the adaptive optics performance degrading toward the shorter wavelengths .
_ however , the fact that the 12.2 @xmath4 m flux of giant planets rapidly declines with time limits the age of the ideal target stars to less then 3050 myr . _
because young stars are typically at 40 pc or beyond , even the highest - order adaptive optics - based systems can only probe the outskirts ( @xmath91 " or @xmath940 au ) of these exoplanetary systems , where giant planets are rare @xcite .
the key novelty of the l  band angular differential imaging is that it is also sensitive to planets as old as a few gyr .
this enables the study of relatively old nearby stars , whose proximity allows us to directly planets on orbits comparable to that of jupiter ( @xmath10  au ) .    exploiting the strength of this technique we are carrying out a 6  pc volume  limited survey of m  stars using the mmt / clio 35 camera ( e.g. @xcite ) . with 14 allocated nights we are covering 35 northern m
 dwarfs within 6  pc .
the m  dwarf survey will complement the sun  like star survey of heinze et al .
( in prep . ) surveying the complete stellar population within 6 pc .
the survey is currently about 2/3 complete and the data reduction and analysis is ongoing ( apai et al .
, in prep . )
we present results from a novel high 
contrast imaging technique .
our naco survey of 21 nearby young stars demonstrates that the giant planet population does not extend beyond 30 au and suggests a cut - off at radius @xmath1 15 au .
most previous imaging surveys have not detected planets because they targeted young stars ( @xmath9 20 pc ) forcing them to probe orbital radii @xmath920  au .
our ongoing mmt 6pc volume  limited survey is probing  for the first time  the massive giant planet population around the closest stars with orbital radii @xmath93 .
baraffe , i. , chabrier , g. , barman , t. s. , allard , f. , & hauschildt , p. h. 2003 , 402 , 701 hinz , p. m. , heinze , a. n .. sivanandam , s. et al . , 653 , 1486 kasper , m. , apai , d. , janson , m. , brandner , w. 2007 , , 472 , 321 lafreniere , d. et al .
2007 , in press , arxiv:0705:4290
we present results from two high  contrast imaging surveys that exploit a novel technique , l  band angular differential imaging . 
 our first survey targeted 21 young stars in the @xmath0  pic and tuc  
 hor moving groups with vlt / naco reaching typical sensitivities of @xmath11  m@xmath2 at @xmath3  au . 
 the statistical analysis of the null result demonstrates that the giant planet population is truncated at 30  au or less ( 90% confidence level ) . 
 our second , on  going mmt / clio survey utilizes the unique sensitivity achieved in the l  
 band for old planets to probe all m  dwarf stars within 6  pc . 
 the proximity of these targets enables direct imaging of planets in orbits like jupiter for the first time  a key step for directly imaging giant planets .