return observable after obtaining promise value

I have the following code but it dos not work, and I would like to return an observable once the promise is resolved. Any ideas? Any suggestion is welcome

  getParalelos() {

    let _observable;
    this.getToken().subscribe(token => {
      _observable = this.http.get(`${this.url}/paralelo?token=${this.token}`, httpOptions)
    })
    return _observable;
  }