Heaviest Element In Stellar Spectra

[BDanielMayfield]

What is the heaviest element as yet detected in any star’s spectrum?

[neufer]

What is the heaviest element as yet detected in any star’s spectrum?

La Silla Telescope Detects Lots of Lead in Three Distant Binaries
European Southern Observatory : 22 August 2001

A high-resolution spectrum of the CH-star HD 196944, obtained with the CES instrument on the ESO 3.6-m telescope in September 2000.

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<<Very high abundances of the heavy element Lead have been discovered in three distant stars in the Milky Way Galaxy. This finding strongly supports the long-held view that roughly half of the stable elements heavier than Iron are produced in common stars during a phase towards the end of their life when they burn their Helium - the other half results from supernova explosions. All the Lead contained in each of the three stars weighs about as much as our Moon. These "Lead stars" - all members of binary stellar systems - have been more enriched with Lead than with any other chemical element heavier than Iron. This new result is in excellent agreement with predictions by current stellar models about the build-up of heavy elements in stellar interiors.

The observed spectrum (dots) shows many absorption lines from elements that are usually seen in stars. The red line shows a model in which elements are present in normal quantities, compared to Iron. The blue line instead shows a model where s-processing takes place during the "AGB" phase of stellar evolution just before an old star expels its gaseous envelope into the surrounding interstellar space and sometime thereafter dies as a burnt-out, dim "white dwarf". It is obvious that only the blue line reproduces the observed absorption line at wavelength 405.781 nm caused by Lead (Pb) atoms in the atmosphere of this star. Stars with masses between 0.8 and 8 times that of the Sun are believed to evolve to AGB-stars and to end their lives in this particular way. At the same time, they produce beautiful nebulae like the "Dumbbell Nebula". Our Sun will also end its active life this way, probably some 7 billion years from now. A subsequent, detailed analysis demonstrated that HD 196944 is a true "Lead star". The new observations are reported by a team of Belgian and French astronomers who used the Coude Echelle Spectrometer on the ESO 3.6-metre telescope at the La Silla Observatory (Chile).>>

[BDanielMayfield]

Pb (lead, element 82) might be tough to beat Art. What prompted my question was this:

Abstract
The thermal evolution of rocky planets on geological timescales (Gyr) depends on the heat input from the long-lived radiogenic elements potassium, thorium, and uranium. Concentrations of the latter two in rocky planet mantles are likely to vary by up to an order of magnitude between different planetary systems because Th and U, like other heavy r-process elements, are produced by rare stellar processes. Here we discuss the effects of these variations on the thermal evolution of an Earth-size planet, using a 1D parameterized convection model. Assuming Th and U abundances consistent with geochemical models of the Bulk Silicate Earth based on chondritic meteorites, we find that Earth had just enough radiogenic heating to maintain a persistent dynamo. According to this model, Earth-like planets of stars with higher abundances of heavy r-process elements, indicated by the relative abundance of europium in their spectra, are likely to have lacked a dynamo for a significant fraction of their lifetimes, with potentially negative consequences for hosting a biosphere. Because the qualitative outcomes of our 1D model are strongly dependent on the treatment of viscosity, further investigations using fully 3D convection models are desirable.

But Eu hardly trumps Pb, as it only has 63 protons.

Can anyone site proof of any element above Pb in stellar spectra?

[Chris Peterson]

Pb (lead, element 82) might be tough to beat Art. What prompted my question was this:

Abstract
The thermal evolution of rocky planets on geological timescales (Gyr) depends on the heat input from the long-lived radiogenic elements potassium, thorium, and uranium. Concentrations of the latter two in rocky planet mantles are likely to vary by up to an order of magnitude between different planetary systems because Th and U, like other heavy r-process elements, are produced by rare stellar processes. Here we discuss the effects of these variations on the thermal evolution of an Earth-size planet, using a 1D parameterized convection model. Assuming Th and U abundances consistent with geochemical models of the Bulk Silicate Earth based on chondritic meteorites, we find that Earth had just enough radiogenic heating to maintain a persistent dynamo. According to this model, Earth-like planets of stars with higher abundances of heavy r-process elements, indicated by the relative abundance of europium in their spectra, are likely to have lacked a dynamo for a significant fraction of their lifetimes, with potentially negative consequences for hosting a biosphere. Because the qualitative outcomes of our 1D model are strongly dependent on the treatment of viscosity, further investigations using fully 3D convection models are desirable.

But Eu hardly trumps Pb, as it only has 63 protons.

Can anyone site proof of any element above Pb in stellar spectra?

I appears that every stable element has been detected in stars, at least up to uranium. This shows the spectroscopically determined abundances of elements from copper to uranium in Sirius A (the black stars) and in the Sun (the blue Sun symbols). Reference.

Update: actually, I note that the graph only shows up to lead for Sirius and to radon for the Sun, but the tabular data in the reference goes up to uranium.
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apjaa2936f6_lr.jpg (58.76 KiB) Viewed 6209 times

[Ann]

Pb (lead, element 82) might be tough to beat Art. What prompted my question was this:

Abstract
The thermal evolution of rocky planets on geological timescales (Gyr) depends on the heat input from the long-lived radiogenic elements potassium, thorium, and uranium. Concentrations of the latter two in rocky planet mantles are likely to vary by up to an order of magnitude between different planetary systems because Th and U, like other heavy r-process elements, are produced by rare stellar processes. Here we discuss the effects of these variations on the thermal evolution of an Earth-size planet, using a 1D parameterized convection model. Assuming Th and U abundances consistent with geochemical models of the Bulk Silicate Earth based on chondritic meteorites, we find that Earth had just enough radiogenic heating to maintain a persistent dynamo. According to this model, Earth-like planets of stars with higher abundances of heavy r-process elements, indicated by the relative abundance of europium in their spectra, are likely to have lacked a dynamo for a significant fraction of their lifetimes, with potentially negative consequences for hosting a biosphere. Because the qualitative outcomes of our 1D model are strongly dependent on the treatment of viscosity, further investigations using fully 3D convection models are desirable.

But Eu hardly trumps Pb, as it only has 63 protons.

Can anyone site proof of any element above Pb in stellar spectra?

I appears that every stable element has been detected in stars, at least up to uranium. This shows the spectroscopically determined abundances of elements from copper to uranium in Sirius A (the black stars) and in the Sun (the blue Sun symbols). Reference.
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apjaa2936f6_lr.jpg

Thanks, Chris, very interesting!

Ann

[BDanielMayfield]

I[t] appears that every stable element has been detected in stars, at least up to uranium. This shows the spectroscopically determined abundances of elements from copper to uranium in Sirius A (the black stars) and in the Sun (the blue Sun symbols). Reference.

Update: actually, I note that the graph only shows up to lead for Sirius and to radon for the Sun, but the tabular data in the reference goes up to uranium.
_
apjaa2936f6_lr.jpg

Thanks Chris, especially for the great reference which I'm enjoying.

[BDanielMayfield]

So uranium, Z=92, half life of most stable isotope U-238 at 4.468×10^9 years, is the heaviest element found in a main sequence star's spectra. But what about kilo or supernova stellar remnants? Is there evidence for any of the trans-uranium elements in stellar explosions?

[neufer]

So uranium, Z=92, half life of most stable isotope U-238 at 4.468×10^9 years, is the heaviest element found in a main sequence star's spectra. But what about kilo or supernova stellar remnants? Is there evidence for any of the trans-uranium elements in stellar explosions?

• 1) Trans-uranium elements are very minor constituents
  2) Interpreting supernova (and/or neutron star collision) spectra is very difficult.

Figure 1. Spectra of SNe, showing early-time distinctions between the four major types and subtypes. The parent galaxies and their redshifts (kilometers per second) are as follows: SN 1987N (NGC 7606; 2171), SN 1987A (LMC; 291), SN 1987M (NGC 2715; 1339), and SN 1984L (NGC 991; 1532). In this review, the variables t and tau represent time after observed B-band maximum and time after core collapse, respectively. The ordinate units are essentially "AB magnitudes."

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Figure 2. Spectra of SNe, showing late-time distinctions between various types and subtypes. The parent galaxy of SN 1987L is NGC 2336 (cz = 2206 km/s); others are listed in the caption of Figure 1. At even later phases, SN 1987A was dominated by strong emission lines of Halpha, O I, Ca II, and the Ca II near-IR triplet, with only a weak continuum.

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2. GENERAL OVERVIEW OF SUPERNOVAE. Spectra
Annu. Rev. Astron. Astrophys. 1997. 35: 309-355

<<Supernovae occur in at least three, and possibly four or more, spectroscopically distinct varieties. The two main classes, Types I and II, were firmly established by Minkowski (1941). Type I SNe are defined by the absence of obvious hydrogen in their optical spectra, except for possible contamination from superposed H II regions. SNe II all prominently exhibit hydrogen in their spectra, yet the strength and profile of the Halpha line vary widely among these objects. Until recently, most spectra of SNe have been obtained near the epoch of maximum brightness, but in principle the classification can be made at any time, as long as the spectrum is of sufficiently high quality. Only occasionally do SNe metamorphose from one type to another, suggesting the use of hybrid designations.

The early-time (t~1 week) spectra of SNe are illustrated in Figure 1. The lines are broad owing to the high velocities of the ejecta, and most of them have P Cygni profiles formed by resonant scattering above the photosphere. SNe Ia are characterized by a deep absorption trough around 6150 Å produced by blueshifted Si II lambda lambda6347, 6371 (collectively called lambda6355). Members of the Ib and Ic subclasses do not show this line. The presence of moderately strong optical He I lines, especially He I lambda5876, distinguishes SNe Ib from SNe Ic (Wheeler & Harkness 1986, Harkness & Wheeler 1990).

The late-time (t ~ 4 months) optical spectra of SNe provide additional constraints on the classification scheme (Figure 2). SNe Ia show blends of dozens of Fe emission lines, mixed with some Co lines. SNe Ib and Ic, on the other hand, have relatively unblended emission lines of intermediate-mass elements such as O and Ca. Emission lines in SNe Ib are narrower (Filippenko et al 1995b) and perhaps stronger (Wheeler 1980) than those in SNe Ic, but these conclusions are based on the few existing late-time spectra of SNe Ib, and no other possibly significant differences have yet been found. At this phase, SNe II are dominated by the strong Halpha emission line; in other respects, most of them spectroscopically resemble SNe Ib and Ic, but the emission lines are even narrower and weaker (Filippenko 1988). The late-time spectra of SNe II show substantial heterogeneity, as do the early-time spectra.

At ultraviolet (UV) wavelengths, all SNe I exhibit a very prominent early-time deficit relative to the blackbody fit at optical wavelengths (e.g. Panagia 1987). This is due to line blanketing by multitudes of transitions, primarily those of Fe II and Co II (Branch & Venkatakrishna 1986). The spectra of SNe Ia (but not of SNe Ib/Ic) also appear depressed at IR wavelengths (Meikle et al 1997). The early-time spectra of most SNe II, in contrast, approximate the single-temperature Planck function from UV through IR wavelengths, with occasionally even a slight UV excess. SN 1987A was an exception: The earliest IUE spectra showed a strong UV deficit relative to the blackbody curve defined at optical wavelengths (Danziger et al 1987), as in SNe I.>>

Identification of strontium in the merger of two neutron stars
[Submitted on 23 Oct 2019]

<<Half of all the elements in the universe heavier than iron were created by rapid neutron capture. The theory for this astrophysical `r-process' was worked out six decades ago and requires an enormous neutron flux to make the bulk of these elements. Where this happens is still debated. A key piece of missing evidence is the identification of freshly-synthesised r-process elements in an astrophysical site. Current models and circumstantial evidence point to neutron star mergers as a probable r-process site, with the optical/infrared `kilonova' emerging in the days after the merger a likely place to detect the spectral signatures of newly-created neutron-capture elements. The kilonova, AT2017gfo, emerging from the gravitational-wave--discovered neutron star merger, GW170817, was the first kilonova where detailed spectra were recorded. When these spectra were first reported it was argued that they were broadly consonant with an outflow of radioactive heavy elements, however, there was no robust identification of any element. Here we report the identification of the neutron-capture element strontium in a re-analysis of these spectra. The detection of a neutron-capture element associated with the collision of two extreme-density stars establishes the origin of r-process elements in neutron star mergers, and demonstrates that neutron stars contain neutron-rich matter.>>

<<In nuclear astrophysics, the rapid neutron-capture process, also known as the r-process, is a set of nuclear reactions that is responsible for the creation of approximately half of the atomic nuclei heavier than iron; the "heavy elements", with the other half produced by the p-process and s-process.

In 2017, entirely new astronomical data about the r-process was discovered in data about the merger of two neutron stars. Using the gravitational wave data captured in GW170817 to identify the location of the merger, several teams observed and studied optical data of the merger, finding spectroscopic evidence of r-process material thrown off by the merging neutron stars. The bulk of this material seems to consist of two types: hot blue masses of highly radioactive r-process matter of lower-mass-range heavy nuclei (A < 140 such as strontium) and cooler red masses of higher mass-number r-process nuclei (A > 140) rich in actinides (such as uranium, thorium, and californium). When released from the huge internal pressure of the neutron star, these ejecta expand and form seed heavy nuclei that rapidly capture free neutrons, and radiate detected optical light for about a week. Such duration of luminosity would not be possible without heating by internal radioactive decay, which is provided by r-process nuclei near their waiting points. Two distinct mass regions (A < 140 and A > 140) for the r-process yields have been known since the first time dependent calculations of the r-process. Because of these spectroscopic features it has been argued that such nucleosynthesis in the Milky Way has been primarily ejecta from neutron-star mergers rather than from supernovae.>>