All Outputs (135)

The effect of starspots on the radii of low-mass pre-main-sequence stars (2014)
Journal Article
Jackson, R. J., & Jeffries, R. D. (2014). The effect of starspots on the radii of low-mass pre-main-sequence stars. Monthly Notices of the Royal Astronomical Society, 441(3), 2111-2123. https://doi.org/10.1093/mnras/stu651

A polytropic model is used to investigate the effects of dark photospheric spots on the evolution and radii of magnetically active, low-mass (M < 0.5 M⊙), pre-main-sequence (PMS) stars. Spots slow the contraction along Hayashi tracks and inflate the... Read More about The effect of starspots on the radii of low-mass pre-main-sequence stars.

The Gaia-ESO Survey: radial metallicity gradients and age-metallicity relation of stars in the Milky Way disk (2014)
Journal Article
Bergemann, M., Ruchti, G. R., Serenelli, A., Feltzing, S., Alves-Brito, A., Asplund, M., …Tautvaišienė, G. (2014). The Gaia-ESO Survey: radial metallicity gradients and age-metallicity relation of stars in the Milky Way disk. Astronomy & Astrophysics, 565, Article A89. https://doi.org/10.1051/0004-6361/201423456

We study the relationship between age, metallicity, and α-enhancement of FGK stars in the Galactic disk. The results are based upon the analysis of high-resolution UVES spectra from the Gaia-ESO large stellar survey. We explore the limitations of the... Read More about The Gaia-ESO Survey: radial metallicity gradients and age-metallicity relation of stars in the Milky Way disk.

AN ANOMALOUS EXTINCTION LAW IN THE Cep OB3b YOUNG CLUSTER: EVIDENCE FOR DUST PROCESSING DURING GAS DISPERSAL (2014)
Journal Article
Allen, T. S., Prchlik, J. J., Megeath, S. T., Gutermuth, R. A., Pipher, J. L., Naylor, T., & Jeffries, R. D. (2014). AN ANOMALOUS EXTINCTION LAW IN THE Cep OB3b YOUNG CLUSTER: EVIDENCE FOR DUST PROCESSING DURING GAS DISPERSAL. Astrophysical Journal, 786(2), 113. https://doi.org/10.1088/0004-637x/786/2/113

We determine the extinction law through Cep OB3b, a young cluster of 3000 stars undergoing gas dispersal. The extinction is measured toward 76 background K giants identified with MMT/Hectospec spectra. Color excess ratios were determined toward each... Read More about AN ANOMALOUS EXTINCTION LAW IN THE Cep OB3b YOUNG CLUSTER: EVIDENCE FOR DUST PROCESSING DURING GAS DISPERSAL.

Gaia-ESO Survey: Properties of the intermediate age open cluster NGC 4815 (2014)
Journal Article
Friel, E. D., Donati, P., Bragaglia, A., Jacobson, H. R., Magrini, L., Prisinzano, L., …Lind, K. (2014). Gaia-ESO Survey: Properties of the intermediate age open cluster NGC 4815. Astronomy & Astrophysics, 563, 1-10. https://doi.org/10.1051/0004-6361/201323215

Context. NGC 4815 is a populous ~500 Myr open cluster at Rgc ~ 7 kpc observed in the first six months of the Gaia-ESO Survey. Located in the inner Galactic disk, NGC 4815 is an important potential tracer of the abundance gradient, where relatively fe... Read More about Gaia-ESO Survey: Properties of the intermediate age open cluster NGC 4815.

The Gaia-ESO Survey: Kinematic structure in the Gamma Velorum cluster (2014)
Journal Article
Jeffries, R. D., Jackson, R. J., Cottaar, M., Koposov, S. E., Lanzafame, A. C., Meyer, M. R., …Maiorca, E. (2014). The Gaia-ESO Survey: Kinematic structure in the Gamma Velorum cluster. Astronomy & Astrophysics, 563, A94. https://doi.org/10.1051/0004-6361/201323288

Context. A key science goal of the Gaia-ESO survey (GES) at the VLT is to use the kinematics of low-mass stars in young clusters and star forming regions to probe their dynamical histories and how they populate the field as they become unbound. The c... Read More about The Gaia-ESO Survey: Kinematic structure in the Gamma Velorum cluster.

Strong biases in estimating the time dependence of mass accretion rates in young stars (2014)
Journal Article
Da Rio, N., Jeffries, R. D., Manara, C. F., & Robberto, M. (2014). Strong biases in estimating the time dependence of mass accretion rates in young stars. Monthly Notices of the Royal Astronomical Society, 439(4), 3308-3328. https://doi.org/10.1093/mnras/stu149

The temporal decay of mass accretion in young stars is a fundamental tracer of the early evolution of circumstellar discs. Through population syntheses, we study how correlated uncertainties between the estimated parameters of young stars (luminosity... Read More about Strong biases in estimating the time dependence of mass accretion rates in young stars.

The Gaia-ESO Survey: Abundance ratios in the inner-disk open clusters Trumpler 20, NGC 4815, NGC 6705 (2014)
Journal Article
Magrini, L., Randich, S., Romano, D., Friel, E., Bragaglia, A., Smiljanic, R., …Worley, C. (2014). The Gaia-ESO Survey: Abundance ratios in the inner-disk open clusters Trumpler 20, NGC 4815, NGC 6705. Astronomy & Astrophysics, 563, A44. https://doi.org/10.1051/0004-6361/201322977

Context. Open clusters are key tools to study the spatialdistribution of abundances in the disk and their evolution with time.

Aims. Using the first release of stellar parameters and abundances of the Gaia-ESO Survey, we analyse the chemical prope... Read More about The Gaia-ESO Survey: Abundance ratios in the inner-disk open clusters Trumpler 20, NGC 4815, NGC 6705.

A lithium depletion boundary age of 21 Myr for the Beta Pictoris moving group (2013)
Journal Article
Binks, A. S., & Jeffries, R. D. (2014). A lithium depletion boundary age of 21 Myr for the Beta Pictoris moving group. Monthly Notices of the Royal Astronomical Society: Letters, 438(1), L11-L15. https://doi.org/10.1093/mnrasl/slt141

Optical spectroscopy is used to confirm membership for eight low-mass candidates in the young Beta Pic moving group (BPMG) via their radial velocities, chromospheric activity and kinematic parallaxes. We searched for the presence of the Li I 6708 Å r... Read More about A lithium depletion boundary age of 21 Myr for the Beta Pictoris moving group.

A lithium depletion boundary age of 22 Myr for NGC 1960 (2013)
Journal Article
Jeffries, R. D., Naylor, T., Mayne, N. J., Bell, C. P. M., & Littlefair, S. P. (2013). A lithium depletion boundary age of 22 Myr for NGC 1960. Monthly Notices of the Royal Astronomical Society, 434(3), 2438-2450. https://doi.org/10.1093/mnras/stt1180

We present a deep Cousins RI photometric survey of the open cluster NGC 1960, complete to RC ≃ 22, IC ≃ 21, that is used to select a sample of very low mass cluster candidates. Gemini spectroscopy of a subset of these is used to confirm membership an... Read More about A lithium depletion boundary age of 22 Myr for NGC 1960.

No evidence for intense, cold accretion on to YSOs from measurements of Li in T-Tauri stars (2013)
Journal Article
Sergison, D. J., Mayne, N. J., Naylor, T., Jeffries, R. D., & Bell, C. P. M. (2013). No evidence for intense, cold accretion on to YSOs from measurements of Li in T-Tauri stars. Monthly Notices of the Royal Astronomical Society, 434(2), 966-977. https://doi.org/10.1093/mnras/stt973

We have used medium-resolution spectra to search for evidence that proto-stellar objects accrete at high rates during their early ‘assembly phase’. Models predict that depleted lithium and reduced luminosity in T-Tauri stars are key signatures of ‘co... Read More about No evidence for intense, cold accretion on to YSOs from measurements of Li in T-Tauri stars.

Pre-main-sequence isochrones – II. Revising star and planet formation time-scales (2013)
Journal Article
Bell, C. P. M., Naylor, T., Mayne, N. J., Jeffries, R. D., & Littlefair, S. P. (2013). Pre-main-sequence isochrones – II. Revising star and planet formation time-scales. Monthly Notices of the Royal Astronomical Society, 434(1), 806-831. https://doi.org/10.1093/mnras/stt1075

We have derived ages for 13 young (<30 Myr) star-forming regions and find that they are up to a factor of 2 older than the ages typically adopted in the literature. This result has wide-ranging implications, including that circumstellar discs survive...

On the relationship between the size and surface coverage of starspots on magnetically active low-mass stars (2013)
Journal Article
Jackson, R. J., & Jeffries, R. D. (2013). On the relationship between the size and surface coverage of starspots on magnetically active low-mass stars. Monthly Notices of the Royal Astronomical Society, 431(2), 1883-1890. https://doi.org/10.1093/mnras/stt304

We present a model that predicts the light curve amplitude distribution for an ensemble of low-mass magnetically active stars, under the assumptions that stellar spin axes are randomly orientated and that cool starspots have a characteristic scale le... Read More about On the relationship between the size and surface coverage of starspots on magnetically active low-mass stars.

Angular momentum evolution of cool stars: Toward a synthesis of observations and theory before and after the ZAMS (2013)
Journal Article
Meibom, S., Barnes, S., Covey, K., Jeffries, R., Matt, S., Morin, J., …Irwin, J. (2013). Angular momentum evolution of cool stars: Toward a synthesis of observations and theory before and after the ZAMS. Astronomische Nachrichten, 334(1-2), 168-171. https://doi.org/10.1002/asna.201211777

The coexistence of fast and slowly rotating cool stars in ZAMS clusters – forming distinct sequences in the color vs. rotation period plane – is providing clues to differences in their pre main-sequence angular momentum evolution. This Cool Stars 17... Read More about Angular momentum evolution of cool stars: Toward a synthesis of observations and theory before and after the ZAMS.

The low-mass Initial Mass Function in the young cluster NGC 6611 (2009)
Journal Article
Jeffries, M. Oliveira, J., D. Jeffries, R., & Th. van Loon, J. (2009). The low-mass Initial Mass Function in the young cluster NGC 6611. Monthly Notices of the Royal Astronomical Society, 1034-1050. https://doi.org/10.1111/j.1365-2966.2008.14140.x

NGC 6611 is the massive young cluster (2-3 Myr) that ionises the Eagle Nebula. We present very deep photometric observations of the central region of NGC 6611 obtained with the Hubble Space Telescope and the following filters: ACS/WFC F775W and F850L... Read More about The low-mass Initial Mass Function in the young cluster NGC 6611.

The Keele–Exeter young cluster survey – I. Low-mass pre-main-sequence stars in NGC 2169 (2007)
Journal Article
Jeffries, R., Oliveira, J., Naylor, T., Mayne, N., & Littlefair, S. (2007). The Keele–Exeter young cluster survey – I. Low-mass pre-main-sequence stars in NGC 2169. Monthly Notices of the Royal Astronomical Society, 376(2), 580 -598. https://doi.org/10.1111/j.1365-2966.2007.11327.x

We have used R_C I_C CCD photometry from the Isaac Newton telescope and intermediate resolution spectroscopy from the Gemini North telescope to identify and characterise low-mass (0.15<M/M_sun<1.3) pre-main sequence stars in the young open cluster NG...

Kinematic structure in the young σ Orionis association (2006)
Journal Article
Jeffries, R., Maxted, P., Oliveira, J., & Naylor, T. (2006). Kinematic structure in the young σ Orionis association. Monthly Notices of the Royal Astronomical Society, 371(1), L6 - L10. https://doi.org/10.1111/j.1745-3933.2006.00196.x

We have used precise radial velocity measurements for a large number of candidate low-mass stars and brown dwarfs, to show that the young Sigma Ori ``cluster'' consists of two spatially superimposed components which are kinematically separated by 7 k... Read More about Kinematic structure in the young σ Orionis association.

Star Formation in the Eagle Nebula and NGC 6611 (2006)
Journal Article
Oliveira, J. M., Jeffries, R. D., & van Loon, J. T. (2006). Star Formation in the Eagle Nebula and NGC 6611. Proceedings of the International Astronomical Union, 2(S237), https://doi.org/10.1017/S1743921307002487

We present IZJHKL' photometry of the core of the cluster NGC 6611 in the Eagle Nebula. This photometry is used to constrain the Initial Mass Function (IMF) and the circumstellar disk frequency of the young stellar objects. Optical spectroscopy of 258... Read More about Star Formation in the Eagle Nebula and NGC 6611.

Circumstellar discs in the young σ Orionis cluster (2006)
Journal Article
Oliveira, J., Jeffries, R., Van Loon, J., & Rushton, M. (2006). Circumstellar discs in the young σ Orionis cluster. Monthly Notices of the Royal Astronomical Society, 369(1), 272 -280. https://doi.org/10.1111/j.1365-2966.2006.10299.x

We present new K- and L'-band imaging observations for members of the young (3-5 Myr) sigma Orionis cluster, obtained with UIST at UKIRT. We determine (K-L') colour excesses with respect to the photospheres, finding evidence for warm circumstellar du... Read More about Circumstellar discs in the young σ Orionis cluster.

Synthesis of the Beryllium 3131A Spectral Region (2005)
Journal Article
Ashwell, J., F. Ashwell, J., Jeffries, R., D. Jeffries, R., & Smalley, B. Synthesis of the Beryllium 3131A Spectral Region. Manuscript submitted for publication

The Beryllium spectral region of the Sun, Procyon and 4 stars in the open cluster NGC6633 up to Teff = 7500K have been synthesised using ATLAS9 model atmospheres and the MOOG spectral synthesis program. The line list used for these syntheses has bee... Read More about Synthesis of the Beryllium 3131A Spectral Region.

The lithium depletion boundary in NGC 2547 as a test of pre-main-sequence evolutionary models (2005)
Journal Article
Jeffries, R. D., & Oliveira, J. M. (2005). The lithium depletion boundary in NGC 2547 as a test of pre-main-sequence evolutionary models. Monthly Notices of the Royal Astronomical Society, 358(1), 13 -29. https://doi.org/10.1111/j.1365-2966.2005.08820.x

Intermediate resolution spectroscopy from the ESO Very Large Telescope is analysed for 63 photometrically selected low-mass (0.08-0.30 Msun) candidates of the open cluster NGC 2547. We have confirmed membership for most of these stars using radial ve... Read More about The lithium depletion boundary in NGC 2547 as a test of pre-main-sequence evolutionary models.