Status of the 24Mg( alpha , gamma ) 28Si reaction rate at stellar temperatures

International audienceBackground: The Mg24(α,γ)Si28 reaction influences the production of magnesium and silicon isotopes during carbon burning and is one of eight reaction rates found to significantly impact the shape of calculated x-ray burst light curves. The reaction rate is based on measured resonance strengths and known properties of levels in Si28. Purpose: It is necessary to update the astrophysical reaction rate for Mg24(α,γ)Si28 incorporating recent modifications to the nuclear level data for Si28, and to determine if any additional as-yet unobserved resonances could contribute to the Mg24(α,γ)Si28 reaction rate. Methods: The reaction rate has been recalculated incorporating updated level assignments from Si28(α,α′)Si28 data using the ratesmc Monte Carlo code. Evidence from the Si28(p,p′)Si28 reaction suggests that there are no further known resonances which could increase the reaction rate at astrophysically important temperatures, though some resonances do not yet have measured resonance strengths. Results: The reaction rate is substantially unchanged from previously calculated rates, especially at astrophysically important temperatures. However, the reaction rate is now constrained to better than 20% across the astrophysically relevant energy range, with 95% confidence. Calculations of the x-ray burst light curve show no appreciable variations when varying the reaction rate within the uncertainty from the Monte Carlo calculations. Conclusion: The Mg24(α,γ)Si28 reaction rate, at temperatures relevant to carbon burning and Type I x-ray bursts, is well constrained by the available experimental data. This removes one reaction from the list of eight previously found to cause variations in x-ray burst light-curve calculations

An investigation of the d(18Ne,19Ne*)p reaction and its astrophysical relevance

The reaction 15 O(alpha; gamma) 19 Ne is one of the potential break­out reactions from the Hot CNO cycle to the rp­process. As such, it may play an important role in nuclear astrophysics for the understanding of energy generation rates and the synthesis of proton­rich nuclei in sites of explosive hydrogen burning, such as novae and X­ray bursters. Experiments were performed at the radioactive ion beam facility, at Louvain­la­Neuve, Belgium, to test the validity of measuring indirectly the 15 O(alpha; gamma) 19 Ne reaction rate. The method utilised was the population of ex­ cited states in 19 Ne and the observation of their ff­decay. Information on the alpha branching ratios of the states of astrophysical interest, just above the alpha­ threshold, allows the reaction rate to be calculated, provided other resonance properties, i.e. T , ER and J , are known. Excited states in 19 Ne were populated via an inverse 18 Ne(d,p) reac­ tion on a deuterated polyethylene target. The reaction and decay products were measured in an experimental set up that comprised three silicon strip detector arrays, with a total of 320 detector elements. Two experiments were performed at E lab = 44.1 MeV and E lab = 54.3 MeV. The recoiling protons tagged the populated state and the detection of a coincident ff­particle and heavy residue pair identified its decay. Branching ratios for several states in 19 Ne were determined, showing the viability of this experimental approach. Optical model parameters were de­ termined from 18 Ne elastic scattering on deuterons. DWBA calculations were performed and compared with experimental angular distributions to yield spectroscopic factors. The results were comparable with a previous meas­ urement using a stable beam, despite the significantly lower beam intensity, and indicated that, provided the necessary beam intensity was available, this method would allow the measurement of the alpha branching ratio of the reson­ ance of most astrophysical interest at 504 keV and thus the determination of the 15 O(alpha; gamma) 19 Ne reaction rate

Nutritional status, growth and disease management in children with single and dual diagnosis of type 1 diabetes mellitus and coeliac disease

Background: The consequences of subclinical coeliac disease (CD) in Type 1 diabetes mellitus (T1DM) remain unclear. We looked at growth, anthropometry and disease management in children with dual diagnosis (T1DM + CD) before and after CD diagnosis.<p></p> Methods: Anthropometry, glycated haemoglobin (HbA1c) and IgA tissue transglutaminase (tTg) were collected prior to, and following CD diagnosis in 23 children with T1DM + CD. This group was matched for demographics, T1DM duration, age at CD diagnosis and at T1DM onset with 23 CD and 44 T1DM controls.<p></p> Results: No differences in growth or anthropometry were found between children with T1DM + CD and controls at any time point. Children with T1DM + CD, had higher BMI z-score two years prior to, than at CD diagnosis (p <0.001). BMI z-score change one year prior to CD diagnosis was lower in the T1DM + CD than the T1DM group (p = 0.009). At two years, height velocity and change in BMI z-scores were similar in all groups. No differences were observed in HbA1c between the T1DM + CD and T1DM groups before or after CD diagnosis. More children with T1DM + CD had raised tTg levels one year after CD diagnosis than CD controls (CDx to CDx + 1 yr; T1DM + CD: 100% to 71%, p = 0.180 and CD: 100% to 45%, p < 0.001); by two years there was no difference.<p></p> Conclusions: No major nutrition or growth deficits were observed in children with T1DM + CD. CD diagnosis does not impact on T1DM glycaemic control. CD specific serology was comparable to children with single CD, but those with dual diagnosis may need more time to adjust to gluten free diet

Stellar Wind Yields of Very Massive Stars

The most massive stars provide an essential source of recycled material for young clusters and galaxies. While very massive stars (VMS, M>100M) are relatively rare compared to O stars, they lose disproportionately large amounts of mass already from the onset of core H-burning. VMS have optically thick winds with elevated mass-loss rates in comparison to optically thin standard O-star winds. We compute wind yields and ejected masses on the main sequence, and we compare enhanced mass-loss rates to standard ones. We calculate solar metallicity wind yields from MESA stellar evolution models in the range 50 - 500M, including a large nuclear network of 92 isotopes, investigating not only the CNO-cycle, but also the Ne-Na and Mg-Al cycles. VMS with enhanced winds eject 5-10 times more H-processed elements (N, Ne, Na, Al) on the main sequence in comparison to standard winds, with possible consequences for observed anti-correlations, such as C-N and Na-O, in globular clusters. We find that for VMS 95% of the total wind yields is produced on the main sequence, while only ~5% is supplied by the post-main sequence. This implies that VMS with enhanced winds are the primary source of 26Al, contrasting previous works where classical Wolf-Rayet winds had been suggested to be responsible for Galactic 26Al enrichment. Finally, 200M stars eject 100 times more of each heavy element in their winds than 50M stars, and even when weighted by an IMF their wind contribution is still an order of magnitude higher than that of 50M stars.Comment: Accepted for publication in MNRAS. 14 pages, 10 figure

X-ray Surface Brightness Profiles of Active Galactic Nuclei in the Extended Groth Strip: Implications for AGN Feedback

Using data from the All Wavelength Extended Groth Strip International Survey (AEGIS) we statistically detect the extended X-ray emission in the interstellar medium (ISM)/intra-cluster medium (ICM) in both active and normal galaxies at 0.3 <= z <= 1.3. For both active galactic nuclei (AGN) host galaxy and normal galaxy samples that are matched in restframe color, luminosity, and redshift distribution, we tentatively detect excess X-ray emission at scales of 1--10 arcsec at a few sigma significance in the surface brightness profiles. The exact significance of this detection is sensitive to the true characterization of Chandra's point spread function. The observed excess in the surface brightness profiles is suggestive of lower extended emission in AGN hosts compared to normal galaxies. This is qualitatively similar to theoretical predictions of the X-ray surface brightness profile from AGN feedback models, where feedback from AGN is likely to evacuate the gas from the center of the galaxy/cluster. We propose that AGN that are intrinsically under-luminous in X-rays, but have equivalent bolometric luminosities to our sources will be the ideal sample to study more robustly the effect of AGN feedback on diffuse ISM/ICM gas.Comment: Accepted in PAS

Coping During the Time of Covid: Mental Health and Changes in Religious Practices

While rituals, particularly religious rituals, have long been the focus of anthropological research, they have only recently become a focus of psychological research. Ritual is defined as 1) predefined sequences of behavior characterized by rigidity, formality, and repetition that are 2) causally opaque, and 3) embedded in a larger system of symbolism and meaning (Hobson et al., 2017; Lawson & McCauley, 1990; Wen et al., 2020). Religious rituals appear to provide three primary regulatory functions for individuals: regulation of emotions, of the performance of goal states, and of social connections (Hobson, et al., 2017). Because of the importance of ritual in emotion regulation, one would expect 1) experiencing an emotional deficit should elicit more ritualistic behavior and 2) enacting rituals should thereby reduce emotional deficits (Hobson, et al., 2017). The current study compared self-reports of anxiety and depression before and during the Covid pandemic with type, frequency, and importance of religious ritual participation. It was hypothesized that, for those for whom religious rituals were an important facet of life, ritual participation would be negatively related to levels of anxiety and depression during the pandemic. Surveys were completed by 122 students at a small, Midwestern liberal arts university. The results indicate that while participation in personal religious behavior such as private prayer and scripture reading did not change during the pandemic, participation in scripted religious rituals did decrease slightly. Both before and during the pandemic individuals rated personal devotional practices such as prayer and scripture reading as more important than participation in personal or corporate religious rituals. Inconsistent with previous research, there was not a relationship between religious belief and behavior with mental health outcomes such as anxiety and depression. Most people who reported an increase in anxiety and depression during the pandemic indicated that at least part of the reason for the increase was their inability to worship in person with others. However, overall depression and anxiety scores were not related to reported increases or decreases in religious ritual participation during the pandemic. Conversely, for those reporting that their anxiety and depression increased at least partly due to the inability to worship publicly with others, changes in depression and anxiety scores were inversely related to continued ritual practices during the pandemic, supporting the hypotheses of this study. Overall, these data indicate a complex relationship among religious ritual participation, personal devotional practices, and mental health outcomes

AEGIS: Chandra Observation of DEEP2 Galaxy Groups and Clusters

We present a 200 ksec Chandra observation of seven spectroscopically selected, high redshift (0.75 < z < 1.03) galaxy groups and clusters discovered by the DEEP2 Galaxy Redshift Survey in the Extended Groth Strip (EGS). X-ray emission at the locations of these systems is consistent with background. The 3-sigma upper limits on the bolometric X-ray luminosities (L_X) of these systems put a strong constraint on the relation between L_X and the velocity dispersion of member galaxies sigma_gal at z~1; the DEEP2 systems have lower luminosity than would be predicted by the local relation. Our result is consistent with recent findings that at high redshift, optically selected clusters tend to be X-ray underluminous. A comparison with mock catalogs indicates that it is unlikely that this effect is entirely caused by a measurement bias between sigma_gal and the dark matter velocity dispersion. Physically, the DEEP2 systems may still be in the process of forming and hence not fully virialized, or they may be deficient in hot gas compared to local systems. We find only one possibly extended source in this Chandra field, which happens to lie outside the DEEP2 coverage.Comment: 5 pages, 3 figures. Accepted for publication in AEGIS ApJ Letters special editio