SQL> select * from v$pwfile_users;

USERNAME SYSDB SYSOP
------------------------------ ----- -----
SYS TRUE TRUE


SQL> show parameter remote_login_passwordfile

NAME TYPE VALUE
------------------------------------ ----------- ----------------------
remote_login_passwordfile string EXCLUSIVE

in sqlnet.ora:

SQLNET.AUTHENTICATION_SERVICES= (NTS)

NAMES.DIRECTORY_PATH= (TNSNAMES, LDAP, EZCONNECT, ONAMES, HOSTNAME)

There is no OSDBA group in OS, there is a ORA_DBA group in OS which contains:

login_username (the local user I use to login)
NT AUTHORITY\SYSTEM