CHANGE IN RATINGSAerCap ( AER) initiated at Morgan Stanley: Morgan Stanley initiates coverage of AerCap with an overweight rating and a $30 price target. Ameristar Casino ( ASCA) downgraded to Hold at Jefferies: ASCA downgraded to Hold rating from Buy at Jefferies. 2007 EPS estimates projected at $1.20 and price target set at $30. Chesapeake Energy ( CHK) downgraded at Goldman Sachs: Goldman is downgrading CHK to Neutral from Buy based on less credit for unbooked resource profit and drilling rig ownership. Also noted that company closed out some hedges in mid-December and has greater risk exposure. Price target cut to $35 from $40. Pacific Sunwear ( PSUN) upgraded at Piper: Piper is upgrading PSUN to an Outperform rating as visibility is improved heading into peak sunwear season. Spirit AeroSystems ( SPR) rated new Neutral at Credit Suisse: Credit Suisse is initiating coverage on SPR with a Neutral rating. Believes company has significant upside but cites potential increase in production rates as a risk. Sets $35 target price. Spirit AeroSystems ( SPR) Holdings initiated at Morgan Stanley: Morgan Stanley initiates coverage of Spirit AeroSystems Holdings with an overweight rating and $38 price target. Seagate ( STX) downgraded at Goldman Sachs: Goldman is downgrading STX to Neutral from Buy due to concern over weak tape during seasonally slow period. See notebook demand running ahead of expectations for December quarter. Price target at $28. T. Rowe Price ( TROW) upgraded at UBS: TROW upgraded to Buy rating from Neutral at UBS. Price target lifts to $52 from $50. Also, introduces 2008 EPS estimate of $2.55.