President of Baseball Operations Dave Dombrowski made the announcement.
Pedroia, 32, was placed on the disabled list on July 25 (retroactive to July 23) with a right hamstring strain, his second DL stint this season due to the same injury (also June 25-July 16). In 75 games for Boston this season, the right-handed batter has hit .287 (87-for-303) with 15 doubles, nine home runs, 34 RBI, and 35 runs scored. From April 26 on, the California native has batted .302 (70-for-232), including a team-best .350 average (28-for-80) in June. He is 48-for-133 (.361) in 34 home games this year. For his major league career, the four-time AL All-Star is a .299 (1,458-for-4,883) hitter with 335 doubles, 13 triples, 115 home runs, and 580 RBI in 1,226 games, all with the Red Sox (since 2006).
Aro, 24, returns for his fourth major league stint with the club, all this season. The Dominican native has appeared in three games for Boston, allowing six runs in 4.2 innings (11.57 ERA) with three strikeouts. He last appeared for the Red Sox on July 1 at Toronto. In his 34 combined appearances between Pawtucket and Double-A Portland, Aro went 3-3 with a 3.04 ERA (25 ER/74.0 IP) and 72 strikeouts. The right-hander also posted a 1.02 WHIP between both levels, allowing 54 hits and issuing 18 walks. Over his last four appearances with the PawSox, he has allowed only two earned runs in 9.1 innings (1.93 ERA) with six strikeouts and no walks. Signed by Boston as an international free agent in June 2011, Aro has gone 16-15 with 13 saves, a 2.84 ERA (95 ER/301.1 IP), and 291 strikeouts in 101 outings (12 starts) over parts of five minor league seasons in the Red Sox system.
Barnes, 25, rejoins the Red Sox for his fifth stint of the season. The right-hander, who has made 23 appearances for Boston this year, including the last two as a starter, is 3-4 with a 6.89 ERA (25 ER/32.2 IP) with 31 strikeouts. Between his two starts for the big league club on August 17 against Cleveland and August 22 against Kansas City, Barnes allowed 11 runs over 10.1 innings, both losses. With Pawtucket this season, the Connecticut native was 1-1 with a 4.06 ERA (17 ER), striking out 41 batters in 37.2 innings over 17 outings (5 starts). Barnes, who made his major league debut with the Red Sox in 2014, is 3-4 with a 6.26 ERA (25 ER/32.2 IP) for his big league career with 39 strikeouts and only 14 walks. Signed by the Red Sox as a first-round selection in the 2011 June Draft, he is 22-25 with a 3.68 ERA (163 ER) and 419 strikeouts in 398.1 innings pitched over 90 career minor league outings (77 starts) from 2012-15.
Hill, 35, signed with the Red Sox as a minor league free agent on August 14 after beginning the 2015 season in the Washington Nationals organization. In 30 Triple-A appearances (5 starts) between Syracuse and Pawtucket, the Boston native combined to go 5-4 with a 2.83 ERA (17 ER/54.0 IP) and .206 opponent batting average, including 3-2 with a 2.78 ERA (10 ER/32.1 IP) in five outings (all starts) with the PawSox. Originally selected by the Chicago Cubs in the fourth round of the 2002 June Draft, Hill began his career as a starting pitcher but has made his last 119 major league appearances out of the bullpen. The left-hander has combined to go 24-22 with a 4.72 ERA (471.0 IP, 247 ER) in 197 major league outings (70 starts) between the Cubs (2005-08), Orioles (2009), Red Sox (2010-12), Indians (2013), Angels (2014), and Yankees (2014), holding left-handed batters to a .216 batting average (98-for-454). In 40 appearances with the Red Sox, all in relief, Hill is 2-0 with a 1.14 ERA, best in club history among those with at least 15.0 innings pitched. He also posted a .217 opponent batting average with Boston, striking out 36 batters and allowing only four earned runs on 25 hits in 31.2 innings pitched.
With these moves, Boston's active major league roster is now at 32, and the team's 40-man roster is now full.