Merge remote-tracking branch 'upstream/master'

Author: rubind

whitepaper/Cosmology/supernovacosmology.tex

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+% ====================================================================
+%+
+% NAME:
+%    M67_special.tex
+%
+% CHAPTER:
+%    specialsurveys.tex
+%
+% ELEVATOR PITCH:
+%    As coeval, equidistant, and chemically homogeneous collections of stars,
+%    open star clusters are ideal for studying the dependence of astrophysical
+%    phenomena on the most fundamental stellar parameters - age and mass.
+%
+% AUTHORS:
+%    Suzanne Hawley
+%    Ruth Angus
+%    Derek Buzasi
+%    Jim Davenport
+%    Mark Giampapa
+%    Vinay Kashyap
+%    Soren Meibom
+%-
+% ====================================================================
+
+\section{A Mini-Survey of the Old Open Cluster M67}
+\def\secname{M67_special}\label{sec:\secname}
+
+\credit{suzannehawley},
+\credit{ruthangus},
+\credit{derekbuzasi},
+\credit{jimdavenport},
+\credit{markgiampapa},
+\credit{vinaykashyap},
+\credit{sorenmeibom}.
+
+\subsection{Introduction}
+
+As coeval, equidistant, and chemically homogeneous collections of stars, open
+star clusters are ideal for studying the dependence of astrophysical phenomena
+on the most fundamental stellar parameters - age and mass.
+Indeed, there are few fields in astronomy that do not rely on results from
+cluster studies, and clusters play a central role in establishing how stellar
+rotation and magnetic activity can be used to constrain the ages of stars and
+stellar populations.
+From an observational perspective, because of their angular extent they are
+accessible to efficient surveys in both imaging and multi-object spectroscopy.
+A selection of clusters representing a sequence in age can be used to
+establish critical empirical relationships such as the dependence of activity
+on rotation, the relationships between activity, rotation and stellar age, the
+evolution of activity cycles, and the nature and evolution of flare
+activity\textemdash{}an urgent area of investigation in view of the potential
+impacts on the structure and evolution of exoplanet atmospheres in systems
+with late-type host stars.
+
+Unfortunately for observers, open clusters dissipate on timescales which are
+generally comparable to stellar evolution timescales on the lower main
+sequence, so older clusters are relatively rare.
+In addition, most clusters lie close to the galactic plane, where determining
+membership is significantly complicated by the large numbers of foreground and
+background stars.
+In this document, we suggest an LSST survey of M67, an open cluster whose
+relative compactness, age, and location above the galactic plane combine to
+make it the ideal cluster for a closer look.
+
+\subsection{Science Case }
+
+The evolution of the rotation rate and magnetic activity in solar-type
+stars are intimately connected. Stellar rotation drives a magnetic
+dynamo, producing a surface magnetic field and magnetic activity which
+manifests as starspots, chromospheric (Ca II HK, H$\alpha$) and coronal
+(X-ray) emission, and flares. The magnetic field also drives a stellar
+wind causing angular momentum loss (\textquotedblleft{}magnetic braking'')
+which in turn slows the rotation rate over time, leading to decreased
+magnetic activity. More magnetically active stars (larger spots, stronger
+Ca II HK, H$\alpha$ and X-ray emission, more flares) therefore tend
+to be younger and to rotate faster. The rotation-age relationship
+is known as gyrochronology, and the correlation between rotation,
+age and magnetic activity for solar-type stars was first codified
+by Skumanich (1972). However, the decrease in rotation rate and magnetic
+field strength over long time-scales is poorly understood and, in
+some cases, hotly contested (Angus et al. 2015, Van Saders et al.
+2016). Recent asteroseismic data from the Kepler spacecraft have revealed
+that magnetic braking may cease at around solar Rossby number, implying
+that gyrochronology is not applicable to older stars (Van Saders 2016).
+
+In addition, the rotational behavior of lower mass stars is largely
+unknown due to the faintness of mid-late type M dwarfs. There is reason
+to believe that M dwarfs cooler than spectral type $~\mathrm{M}4$
+may behave differently from the G, K and early M stars, since that
+spectral type marks the boundary where the star becomes fully convective,
+and a solar-type shell dynamo (which requires an interface region
+between the convective envelope and radiative core of the star) can
+no longer operate. Using chromospheric H$\alpha$ emission as a proxy,
+West et al. (2008) studied a large sample of M dwarfs from SDSS and
+showed that magnetic activity in mid-late M dwarfs lasts much longer
+than in the earlier type stars.
+
+The difficulties inherent in understanding the evolution of stellar
+rotation and activity on the lower main sequence are further increased
+by our inability to obtain accurate ages for field stars with ages
+comparable to that of the Sun, which appears to be just the range
+of ages for which our understanding of the phenomena are most suspect.
+While asteroseismology can address this situation with exquisite precision,
+it can only do so for the brighter stars accessible to space missions
+such as Kepler. Making use of older open clusters is a way to fill
+this gap.
+
+The solar-age and solar-metallicity open cluster, M67, is a benchmark
+cluster for understanding stellar evolution and the nature of late-type
+stars at solar age. M67 is unique due to its solar chemical composition,
+the fact that it is relatively nearby ($\sim900$ pc), and its relatively
+low extinction due to its location above the galactic plane. Extensive
+proper motion, radial velocity and photometric surveys have been carried
+out (e.g., Girard et al. 1989, Montgomery et al. 1993, Yadav et al.
+2008, Geller et al. 2015), while Giampapa et al. (2006) conducted
+a survey of chromospheric activity in the solar-type members of M67
+which yielded interesting insights on the range of magnetic activity
+on sun-like stars in comparison with the range exhibited by the Sun
+during the sunspot cycle. ÷nehag et al. (2011) find that solar twins
+in M67 have photospheric spectra that are virtually indistinguishable
+from the Sun\textquoteright{}s at echelle resolutions.
+
+Located in the sky at approximately $\mathrm{RA}=9\mathrm{h}$ and
+$\mathrm{Dec}=+12^{\circ}$, M67 is an exceptionally meritorious and
+accessible candidate for an LSST mini-survey, which would also enable
+productive follow-up observations by an array of OIR facilities. LSST
+observations of M67 would yield data on the rotation periods and variability
+of its members at high precisions, particularly for dwarfs later than
+about K0 ($V>16$). Little is known about the nature of variability
+on short and long time scales for low-mass dwarfs at solar age. For
+example, the frequency of \textquoteleft{}superflaring\textquoteright{}
+at solar age could be investigated for the first time. Furthermore,
+the combination of LSST observations and OIR synoptic datasets for
+M67 would enable the characterization of the conditions of the habitable
+zones in late- type stars at solar age.
+
+In addition to sun-like stars, M67 includes an array of interesting
+objects such as blue stragglers (Shetrone \& Sandquist 2000), an AM
+Her star (Gilliland et al. 1991, Pasquini et al. 1994), a red straggler,
+two subgiants (Mathieu et al. 2003), and detected X-ray sources due
+to stellar coronal emission (e.g., Pasquini \& Belloni 1998). Davenport
+\& Sandquist (2010) found a minimum binary fraction of 45\% in the
+cluster. Other investigations include studies of the white dwarf cooling
+sequence (Richer et al. 1998), angular momentum evolution near the
+turnoff (Melo et al. 2001), and the behavior of key light elements
+such as lithium and beryllium (e.g., Randich et al. 2007).
+
+
+\subsection{Observing Plans }
+
+Performing the mini-survey of M67 which we advocate would require
+two modifications to the baseline LSST operations mode. LSST does
+not plan to observe as far north as $\mathrm{Dec}=+12^{\circ}$ in
+its main survey, but the M67 field should certainly be accessible
+for a mini-survey as a single pointing. Since imaging the entire cluster
+would require less than a single LSST field, we view this additional
+pointing as being of minimal inconvenience relative to the expected
+scientific gain. As we anticipate rotation periods ranging from $\sim\mathrm{days}$
+up to several months, we would require sampling over all of these
+timescales, though it need not be continuous.
+
+A second potential complication is that the cluster is relatively
+bright. While dwarfs below about spectral K0 in M67 are fainter than
+the LSST bright limit of $\sim16$, the cluster G dwarfs will saturate
+the LSST detectors in a 15-second integration. We suggest two alternative
+approaches to address this issue. First, if the short exposure surveying mode
+suggested elsewhere in this document (Section \ref{sec:shortexp}) is adopted,
+then the new LSST minimum exposure time of 0.1 seconds would easily
+accommodate the entire M67 main sequence. Alternatively, or if the
+short exposure mode is not adopted, we note that work with the Kepler
+mission (e.g., Haas et al. 2011) has shown success using custom pixel
+masks to accurately perform photometry on stars as much as 6 magnitudes
+brighter than the saturation level. Similar techniques applied to
+the LSST fields should enable photometry for the G dwarfs, particularly
+those in less-crowded portions of the field.
+
+\navigationbar

whitepaper/SpecialSurveys/M67_special.tex

@@ -19,7 +19,7 @@
 
 % \section{Cataclismic Variables}
 \subsection{Cataclismic Variables}
-\def\secname{CVtransients}\label{sec:\secname}
+\def\secname{\chpname:CVtransients}\label{sec:\secname}
 
 \credit{paulaszkody},
 \credit{fedhere}
@@ -41,7 +41,7 @@ \subsection{Cataclismic Variables}
 shortest period dwarf novae and the recurrence times in recurrent novae). The
 amplitudes range from tenths of mags for flickering and pulsations to 4 mags
 for normal dwarf novae and changes in novalike states up to 9-15 mags for the
-largest amplitude dwarf novae and regular novae.
+largest amplitude dwarf novae and classical novae.
 
 These large differences make correct classification with LSST difficult
 but necessary in order to reach goals of assessing the correct number