The FERRUM project: experimentally determined metastable lifetimes and transition probabilities for forbidden [Ti ii] lines observed in η Carinae

Abstract

In the spectrum of an emission‐line region ejected from the massive star Eta Carinae, called the strontium filament (SrF), forbidden lines from many elements, in particular [Sr ii] and [Ti ii], are observed. These lines are strong in this specific region and valuable for plasma diagnostics. Forbidden lines are not easily produced in laboratory light sources and the atomic parameters for these lines can thus not be measured in a straightforward way. We use a combination of laboratory and astrophysical measurements to determine transition probabilities for the [Ti ii] lines. Lifetimes for metastable levels in Ti ii are measured using a laser probing technique on a stored ion beam at CRYRING, MSL, Stockholm. Branching fractions from some of these levels are derived from Hubble Space Telescope/STIS spectra of the SrF. The astrophysical branching fractions are combined with the experimental lifetimes to determine absolute transition probabilities. We report lifetimes for the Ti ii levels b4P3/2, b2P1/2, c2D3/2 and c2D5/2, in the range 0.29–17 s, and transition probabilities for eight parity‐forbidden lines from the levels c2D3/2 and c2D5/2, along with uncertainty estimates.

The FERRUM project: experimental and theoretical transition rates of forbidden [Sc II] lines and radiative lifetimes of metastable Sc II levels

“…This region was given the name "Strontium Filament" (SrF) from the identification of [Sr ii], which previously was not observed in any other astronomical object (Zethson et al 2001). In a previous paper Hartman et al (2005) derived A-values for [Ti ii] with these spectra. Photoionization modelling indicate peculiar abundance patterns and photo-excitation in this region (Bautista et al 2002(Bautista et al , 2006.…”

Laboratory transition probabilities for studies of nucleosynthesis of Fe-group elements1

“…Hartman et al [16] subsequently extended this work to forbidden lines of Ti II using Ti + ions in the metastable 3d 2 ( 3 P)4s b 4 P 5/2 level with a very long lifetime of 23s! Measurements on forbidden lines of Ti II were immediately applied in studies of Eta Carinae by Hartman et al [17]. Hartman et al [18] extended earlier work at CRYRING to Sc II, combined the radiative lifetimes of metastable levels with BFs from observations of Eta Carinae, and determined transition probabilities of forbidden lines in Sc II.…”

Theoretical investigation of oscillator strengths and lifetimes in Ti II

“…The energy levels of Ti ii presented in the Atomic Spectra Database (ASD) of the National Institute of Standards and Technology (NIST; see Kramida et al (2019)) were compiled by Sugar & Corliss (1985) and Saloman (2012) based on the re- The full table of Table 3 is available in electronic form at the CDS via the anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/ sults from Huldt et al (1982). The observed spectral lines of Ti ii were compiled from sources of Huldt et al (1982), Allende Prieto & Garcia Lopez (1998), Pickering et al (2001), and Aldenius (2009) for electric dipole (E1) transitions and of Hartman et al (2004Hartman et al ( , 2005 and Bautista et al (2006) for magnetic dipole (M1) and electric quadrupole (E2) transitions.…”

“…There are a number of experimental and theoretical studies of lifetimes and oscillator strengths of the Ti ii ion. The sources adopted in the compilation by the NIST ASD are summarised in Table 1, and they include those of Roberts et al (1973), Roberts et al (1975), Wolnik & Berthel (1973), Danzmann & Kock (1980), Kostyk & Orlova (1983), Pickering et al (2001), Wiese et al (2001), Morton (2003), Hartman et al (2005), and Deb et al (2008).…”